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Would it work to inject CO2 in this manner?

Discussion in 'CO2 Enrichment' started by jeremy v, Sep 29, 2008.

  1. jeremy v

    jeremy v Guru Class Expert

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    Hello,

    I am slowly gathering ideas and designing within my head what will eventually become a small planted tank room in my home. It is going to be a small room about 10'x10' or so and have 3-4 main display tanks that look through the walls of the room into the living areas of the home.

    I have been looking into all sorts of ways to inject CO2 into the tanks and there are good solutions for the large display tanks, but I would also like to have 4-5 small (10 gallon or so) tanks in the room just for plant grow out and nutrient testing purposes.

    I am trying to figure out a way to make all the tanks pretty consistent in their CO2 levels and trying to find way to simplify the CO2 setup.

    This is my idea, let me know if there is a problem I am not seeing.

    I am thinking of having a single 20lb CO2 tank with a regulator and solenoid and having the tank just sitting in the room. I would design at least one level of redundancy into the setup. Most likely by having two parallel pathways for the CO2 to travel, and two solenoids on each pathway. That way if one solenoid fails it only cuts off one pathway, and if one gets stuck open the second solenoid along the same pathway still shuts off the CO2 flow when necessary. Then have an air CO2 level controller (like they use for hydroponics and greenhouses) set at a certain level of CO2 for the room air itself. I can then adjust the concentration of CO2 in the room air to what is necessary to provide the tanks with their 30ppm of "equilibrium with tank room air" CO2.

    From what I have been reading, I can increase the CO2 in the air to 1% (10,000ppm) without any danger to myself when I am in the room. Levels need to be around 70,000-100,000ppm before there start to be issues with humans. That is a minimum of a 7x safety factor for me being in the room, and it means that something would really have to be off for there to ever be any danger associated with CO2 levels being too high. Even 10,000ppm is about 25 times equilibrium, so I should be able to safely and easily get my 30ppm in the water.

    If the room is sealed off from the rest of the house well would this work? Has anyone done it before?

    Would it use much more or less CO2 than running bubble counters to each tank individually and having single (or multiple) reactors in each tank?

    I am thinking of having a bathroom type ceiling fan that possibly evacuates the air in the room each night after lights off and replaces it with new fresh air. Just have it on a timer or something. I could possibly have that air go to a future greenhouse I am thinking of building to boost the CO2 levels in there and provide a little bit of extra warm air to the outdoor greenhouse in the winter. That way I could work on cleaning the tank filters and stuff at night and be breathing in normal air if I was nervous about the increased CO2 levels (and their effect on me) at all.

    It seems like a much more simple setup to me, because then it only requires the absolute minimum of stuff, no reactor for each tank, multiple bubble counters, manifolds, multiple drop checkers, etc.

    I could possibly have a second CO2 monitor in the room that turns on a fan or opens a vent if the CO2 gets higher than a predetermined set level to prevent it from ever getting too high to be safe for fish or humans. That would be a good piece of redundancy in the system.

    Wouldn't it be the same thing as basically making the whole fish room into one big "bell type" diffusor?

    I am thinking that I could then agitate the tanks really well to keep oxygen levels high for the fish, and not have any outgassing of CO2 at all to maintain ~30ppm CO2 in the tanks. I would just need a fan in the room to keep the CO2 distributed really well within the small room.

    I could even put an air pump in the room that draws air from the room and puts it through the airstones. Then I can put a few airstones into each of the tank filters to help keep CO2 levels in the tanks stable and to help make sure enough CO2 is in the tanks at all times. If one particular tank was having a hard time getting CO2 fast enough I would only need to add a few more airstones into that tank's filter to boost the available CO2 and the amount of CO2 diffusion into the water.

    I am thinking about this, because with this setup I would only have one thing to check and keep tabs on to make sure all of my CO2 levels are perfect wouldn't I?

    The air CO2 meters I have been looking at are all accurate to within 1% as well, so I would think my accuracy of knowing exactly how much CO2 is in my tanks would be much greater than with a reactor and a drop checker method.

    I would appreciate any experiences, comments, criticisms of this type of a setup. I am only in the dreaming/planning stages right now so anything is open to change.

    Have a good one, Jeremy
     
  2. tedr108

    tedr108 Lifetime Charter Member
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    Very interesting idea, Jeremy. I'm looking forward to the responses.

    I was thinking that another way to have only one thing to deal with would be to tie all of the tanks together with plumbing -- have one main "reactor" tank for the CO2 (a sump sort of thing -- just a big one for all of the tanks). An advantage of this method is that fertilizers would only have to be put in one place. A disadvantage is that any algae or disease outbreaks would go to all of the tanks!
     
  3. jeremy v

    jeremy v Guru Class Expert

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    Tedr108,

    That is a good idea, but it won't work in my case. There are some other factors that I probably should have added in my original post.

    1- I want to be able to have all the tanks independent from each other to keep all the fish as safe from disease as possible like you mentioned.

    2- I want to have some low light and some medium/high light tanks, so I would like to be able to tailor or adjust the fertilizers for each tank individually if necessary.

    3- I want to be able to adjust the kH or gH of tanks individually so that I can have tanks with soft water fish and other tanks with hard water fish if desired.

    4- I want to be able to have any algae outbreaks or problems associated with the balances in tanks being off to only affect one tank and not all the tanks at once. CO2 would be the only thing that could affect all tanks equally, but it would still affect the low light tanks less, so I should be able to catch any problems before it affects all the tanks.

    5- I have designed a constant water change setup that drips new water into each tank at a certain rate and I want to be able to change that rate into each tank individually. That way I can do a 10-20% weekly water change max on the low light tanks and a 50% weekly (with dilution taken into account) on the medium/high light tanks, etc. I can't do that if they all share the same water.

    Have a good one, Jeremy
     
  4. VaughnH

    VaughnH Lifetime Charter Member
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    It is certainly an interesting idea. I doubt that you can make the room airtight, and it would have to be to avoid losing a lot of CO2 into other areas of the house or outdoors. And, I'm not sure what the relationship is between partial pressure of CO2 in air and ppm of CO2 in water that is always in contact with that air. If that relationship is favorable, and you can adequately seal the room (you would need a relief valve to avoid collapsing or ballooning the room) to keep the CO2 in the room, it should be a very good system. The room would also be at 100% humidity at all times, so condensation would be a major problem.
     
  5. jeremy v

    jeremy v Guru Class Expert

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    Vaughn,

    They do this in Controlled Environment Agriculture (CEA), so I will have to look more deeply into how they keep the CO2 in the greenhouses successfully.

    Does anyone have any insight on this? I have been trying to find an equation relating the concentration of CO2 in air to the corresponding equilibrium concentration in water. That will be key to this working or not. From what I have found so far, it seems like temperature and pressure change the solubility but that's it. Would that mean that the two would be linearly related? So would that mean that doubling the CO2 in the fish room air would also double the dissolved CO2 in the aquariums?

    I am thinking of setting it up like lots of fish breeders do with glass lids on everything. Then I get the CO2 into the tanks by using lots of airstones in the filter tanks. The air pump would pull air high in CO2 from the fish room, so it should work for putting the extra CO2 into the tank water. I am thinking that would cut down on moisture a lot.

    I also have two other alternatives and I ask for all of your input on them.

    1- Small dehumidifier- it would most likely draw less electricity than all the individual reactors would draw. It would also draw less than the main aquarium pumps would draw (from needing larger pumps to power mazzei's).

    2- Dri-Z-Air- This one seems like the nicest setup in my mind. I looked at the MSDS for Dri-Z-Air and it is just pure CaCl2. You put it in a small moisture collection container and it pulls the moisture from the air. I could just measure out tank dosing quantities of CaCl2 into several little water traps throughout the fish room, and then let the CaCl2 suck up the air's humidity. Then I can just dump the collected water mixed with the liquefied Dri-Z-Air into the display tanks each week. It would keep the fish room humidity down and also dose the Calcium the plants need to the tank at the same time, haha. Oh if it could only work as well as it can be explained.

    Any other ideas would be greatly appreciated, and thanks to all for the input so far. The more I am researching this the more it seems like it could work, and work really well too.

    Have a good one, Jeremy
     
  6. VaughnH

    VaughnH Lifetime Charter Member
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    You can't pump air into a sealed top aquarium without building up pressure in the aquarium. If you relieve the pressure you let the water vapor out as well as the air.

    The dehumidifier would be helpful, but the sealed room would reach an equilibrium on water vapor just as it would with CO2. I think the dehumidifier would just be effectively slowly pumping the water out of the tanks.
     
  7. jeremy v

    jeremy v Guru Class Expert

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    Vaughn,

    I just meant using the regular pre-made glass flip-top lids on the tanks instead of them being open-topped tanks, not actually sealing the tops of the tanks airtight. There would be no pressure build-up at all. The water vapor would still leave from the air stone bubbles escaping the lid, but the tanks would have very little evaporation from the water surface adding to the moisture in the air. On my 75, if I run it without any lid it evaporates about a gallon of water a day from the tank surface, but with a glass flip-top lid it only evaporates about a gallon a week at most. Adding airstones into the same tank doesn't change that evaporation rate much at all (1 gallon every 5 days with a 12" long fine bubble wall in the tank), and it still remains much less total evaporation than I would have with an open top tank. That's all I was thinking.

    I don't understand this Vaughn and maybe I am missing something here, can you explain this further? I was thinking that since my CO2 levels will be at most 2% of the total air volume in the room that the air pressure in the room would pretty much stay exactly the same. It would only at most increase in pressure by 2% wouldn't it? That would just put a very slight positive pressure on the walls of the room and would most likely only be enough to leak air out of the room (if there was a crack or hole in the wall somewhere) instead of it coming in the room and that's about it.

    I was just thinking it would work like the air handling systems in hospitals. They have it so that all the rooms that house people that can't handle any exposure to pathogens of any type are positively pressurized with heavily cleaned air, so that even a small leak in the wall somewhere leaks clean air out (instead of dirty air from somewhere else in the hospital leaking into the room). Then regular hospital rooms are negatively pressurized so that any leaks in the wall or open doorways very slowly pull air from the hospital hallways into the rooms. That helps to keep anyone's infection or pathogen isolated to only their room so that it can't spread throughout the rest of the hospital very easily through the air.

    On another note, I have to scrap my idea for evacuating the room every night and replacing the air fresh each morning. I did the calcs, and it seems that I would need a CO2 level in the air of a little more than 20,000ppm to have a 30ppm equilibrium with the water. That was a calc done using Henry's Law. That makes sense, and if my calcs were right, at constant temperature and pressure the relationship between air concentration and equilibrium water concentration is linear, so doubling what is in the air also doubles what is in the water at equilibrium.

    Needing ~20,000ppm is the same as needing 2% of my air volume to be CO2. A 10x10x8 room is 800ft3, so that means I would need about 16ft3 of CO2 gas a day to fill that room to 2% CO2 if I replaced the air with fresh each night. That is a little less than 2 lbs of liquid CO2 each day, so a 20lb CO2 tank would only last a little over 10 days. That's a lot of waste. I could use a lot less CO2 by not refreshing the room air and starting over each night, but I need to do some more calcs related to oxygen levels to see if that is feasible.

    20,000ppm of CO2 is a little more than half the concentration of CO2 in exhaled human breath (~35,000ppm or 3.5% for human exhaled air). As far as I have been able to find that is still a perfectly safe CO2 level in my application, so I will continue to look into this a little further and then weigh all the pros and cons with all the other options out there and see what fits best with what I am wanting to achieve with my future tank room.

    If anyone else has any comments or is seeing anything I have missed related to using this method let me know. I am finding that this technique might not work how I want it to, but not because of the calcs or principals being wrong. They have greenhouse CO2 controllers that can control and regulate CO2 levels up to 10,000ppm CO2, but I have not yet found one that can go up to 20,000ppm. That will be a necessary thing to find for this to be able to work. Otherwise I might be stuck with ~15ppm equilibrium CO2 being the highest CO2 level I can accurately reach in the tanks. That would work though if I stayed with lower light tanks, which I might do anyways.

    Have a good one, Jeremy

    P.S.- CO2 levels in buildings and room air is usually measured only as an indication of the freshness of room or building air, and having levels 1000ppm of CO2 or higher is an indication that the room doesn't have very good overall air circulation with the outdoors. It is not the CO2 that gives you the possible health effects though, it is the build-up of other byproducts of human respiration or chemicals in the air that can be mildly harmful when CO2 is at that level. CO2 is just a very easy thing to measure compared to the other byproducts of human respiration and/or radon from the ground, etc.

    That's why I am saying that CO2 at 10,000ppm or above is still safe for humans even though many sites say that 1000ppm and above is not good for health. I just thought I would mention it in case anyone was thinking I was off by a factor of 10 in my acceptable CO2 levels.
     
  8. VaughnH

    VaughnH Lifetime Charter Member
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    The reason you might need a two way relief valve is that a sealed room subjected to normal barometric pressure changes might not be able to withstand the forces involved. Normal atmospheric pressure changes from around 29.5 inches Hg to around 30.5 inches Hg, with some peaks going beyond that. So, one inch of mercury is about one half pound per square inch, or 72 pounds per square foot, or 720 pounds of force on a ten square foot wall or floor or ceiling. An 8 foot by 12 foot room, with an 8 foot ceiling height would have 96 square foot of surface on two walls, the floor and the ceiling. That gives 6912 pounds of force on those surfaces. When I lived in Missouri, a barometric pressure drop or rise of 1 inch of Hg wasn't all that unusual.

    All things considered, if you can verify that the elevated CO2 level is not going to harm humans, I think you should give this a try. The problems are all surmountable.
     
  9. jeremy v

    jeremy v Guru Class Expert

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    Vaughn,

    I never thought about that, thank you for letting me know. I thought you were referring to the pressure created from the CO2 gas adding to the air in the room.

    In relation to the room being sealed and still being able to adjust relative pressure to account for changes in atmospheric pressure, could I make a sort of flexible accordion type of plastic device that is circular and in the ceiling of the room? Make it so that when the pressure increases outside the room the accordion that is filled with extra fish room air deflates on its' own to increase the air pressure in the room until they are equalized. Then when the pressure outside lessens the accordion expands and fills with some of the fish room air until the fish room is again the same as outside. If that would work I am thinking it would be perfect, because then no CO2 would be lost from the room during pressure changes, the accordion would just expand and contract a little bit.

    How much more air volume can fit in 800ft3 once the atmospheric pressure increases by 1in Hg? That's the question I need to find the answer to in order for me to know how large the accordion would need to be.

    I am also starting to think that I might not need to actually air out the room at all other than occasionally just to refresh the air, and just in case the CO2 levels get too high. I was originally thinking it would be necessary to keep the oxygen levels up for the fish. If plants are net producers of oxygen though, I should theoretically see a slow increase in oxygen in the sealed fish room air over time wouldn't I? Essentially the CO2 that I am putting into the room would be absorbed by the plants and then net oxygen would be released adding to what is already in the room. The oxygen equilibrium would work backwards and the tanks would become high in O2. That would outgas to the room until a new higher equilibrium was again reached. That would mean that I would be able to drop the use of CO2 tremendously from my previous calcs, because if the room is sealed well all that would be lost would be the small amount lost out the door from entering the room each day to feed the fish and perform maintenance. Even that would be somewhat balanced out since the human breath is 35,000ppm CO2, so just working in the room for a 15 minutes or so each day would most likely make up for most of the CO2 lost from opening the door really quickly.

    This is getting really interesting to me. It would be really nice to have a fish room where I could just set up as many tanks anywhere within the room that I want without having to set up any reactors, bubble counters, etc. I could know that they will all end up at 30ppm CO2 within 24 hrs. or so as long as the room air is held at the right concentration of CO2 and the tanks are well aerated with the high CO2 room air.

    You are right Vaughn, I should look more deeply into the health affects of the higher CO2 levels. I want to be extra sure I will be safe, and also know fully what my risks are. I also want to make sure that a child or elderly person could go in the room without problems as well, since they would most likely be more sensitive to altered air. Carbon dioxide is heavier than air, but it should stay well mixed with the air just from the small fan that would be circulating the air in the room keeping the CO2 concentration equal everywhere. I want to make sure the bottom foot or so of air wouldn't become a low oxygen and very high CO2 zone for a crawling child or something if the fans ever quit on me, the CO2 all settled in the room, and someone went in the room that wasn't supposed to be there.

    Have a good one, Jeremy
     
  10. VaughnH

    VaughnH Lifetime Charter Member
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    PxV=constant x Temperature. If the pressure goes from 29.5 inches of Hg to 30.5 inches of Hg, the volume goes to: P1V1=P2V2, V2=P1V1/P2=29.5xV1/30.5=.967V1. So, for that rise in barometric pressure, the volume of air in the room would decrease by about 3.3%, which, for 800 cu foot, is 26 cu ft. You would, therefore need an accumulator holding 26 cu ft to hold the air that would be forced in by the higher atomospheric pressure, or forced out by the lower atmospheric presssure. If you used a big neopene weather balloon for the accumulator it would have to be capable of being blown up to 1.84 ft in radius, or 44 inches in diameter, easy to do. Of course that balloon would need to be kept out of direct sunlight to avoid UV damage to it.

    This could be a really fun project!
     
  11. jeremy v

    jeremy v Guru Class Expert

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    I am starting to get more and more excited about trying this.

    Here is the stuff I found on CO2 toxicity. It was collected from a few different hazmat websites, OSHA and NIOSH rules related to workplace CO2 exposure, and the MSDS sheet for CO2.

    1- At 1% concentration of carbon dioxide CO2 (10,000 parts per million or ppm) and under continuous exposure at that level, some occupants are likely to feel drowsy.

    2- Above 2%(20000ppm), carbon dioxide may cause a feeling of heaviness in the chest and/or more frequent and deeper respirations. This is due to there being less of a difference in CO2 levels between the air being inhaled and the air being exhaled.

    3- Breathing rate doubles at 3% CO2 and is four times the normal rate at 5% CO2. 3.5% is the amount of CO2 exhaled in the average breath, so it makes sense that levels higher than that would make it so you would have to breathe faster to still be able to eliminate the CO2 from your body that you need to eliminate.

    4- Toxic levels of carbon dioxide: at levels above 5%, concentration CO2 is directly toxic. [At lower levels we may be seeing effects of a reduction in the relative amount of oxygen rather than direct toxicity of CO2.]

    I am assuming that is because human breathing is now adding CO2 to the body instead of removing it from the body since the concentration in the air is now more than the concentration of average human exhaled breath. That would mean that breathing would be adding CO2 to the body and causing acidosis. That makes perfect sense and is good to know, because some other sites (one of which I think was wikipedia) mentioned that levels up to 70,000ppm were not poisonous and that didn't make sense when we breathe out 35,000ppm.

    This all means that 3.5% or 35000ppm should actually be my absolute max safe level for CO2 in the room. Anything less than that level and the main side effect is that I might need to breathe a little harder to still be able to eliminate the CO2 from my lungs effectively.

    I am still thinking of trying this, but I will most likely set it all up for 15ppm CO2 in the water and an air concentration of 10-12000ppm at first and only grow plants under lower light levels. Then if I want I can slowly try upping the CO2 to see if there are any issues that arise that make me uncomfortable with this setup healthwise.

    Thanks Vaughn for the calcs on the volume of air needed within the expanding balloon to balance out barometric pressure changes. That seems very doable to me. I could just have the balloon in the attic of the house and attached with an air tight seal to the ceiling of the fish room. That would be pretty easy to do. Then I would just set it all up on a day that has the highest barometric pressure possible.

    I was thinking though that anytime I opened the door to the room the pressures would be instantly equalized and the equalizing balloon would deflate. Then if the outside barometric pressure increased (after the door was closed again) the balloon might invert itself down into the fish room as the pressure tries to equalize. What might work better would be a flexible membrane on the ceiling that is a large disc shape. That way when the door is opened it always returns to center as its' resting position. Then if the barometric pressure rises or drops after the door is again shut the membrane flexes down slightly into the room or else bows up slightly into the attic to equalize the pressure.

    Equalizing the pressure at all times would ensure that it was always nice and easy to open the door to the room too, haha.

    I guess the next step would be to see if I would need any sort of a special wall paint, coating, etc. to ensure that the CO2 couldn't diffuse itself slowly through the walls and into the rest of the house. I would think that just painting the room walls with a waterproof epoxy would be a very safe bet, and that would protect against damage from humidity as well.

    Have a good one, Jeremy
     
  12. VaughnH

    VaughnH Lifetime Charter Member
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    Just to brainstorm this: Suppose you used a piece of sonotube Concrete Accessories, Bozeman Montana -> Sonotube, 36 inches in diameter, and about 36" long, extending up into the "attic" above the room, with a weather balloon mounted with the opening in the middle of the length of sonotube. That way the expanded balloon would always be contained in the sonotube and it would act like a rolling piston to change the "accumulator" volume. As the room pressure rises above atmospheric pressure the balloon expand upwards, and as the room pressure drops below atmospheric pressure, it expands downward towards the room. The hole in the ceiling connecting to the sonotube accumulator could be as small as a couple of inches in diameter or so.
     
  13. jeremy v

    jeremy v Guru Class Expert

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    Vaughn,

    That's a great idea. I like that design. It is simple, inconspicuous, and effective in all situations. I think the most well engineered stuff uses the least amount of parts possible and still effortlessly achieves the purpose required of it. That setup would do just that.

    I agree with you, I could have a nice small hole in the ceiling, because all I am doing is equalizing pressure, not actually moving much air through the hole. I have used sonotube for lots of stuff in the past, so I am very familiar with it's limitations and attributes. If I remember correctly, I think sonotube uses a light polymer type coating of some sort on the inside of the tube, and most other brands of the same cardboard concrete tubing use a light spray of wax.

    I think I like your idea, but instead of using sonotube, using corrugated plastic (HDPE) culvert pipe. They have pipes that are made with two layers of HDPE melted together, so they are corrugated on the outside and smooth on the inside. You can get it in all common sizes up to at least 5' in diameter. That would ensure humidity would never become a problem, which would be a long term weakness of the sonotube since it is only a lightly coated cardboard on the inside and just bare cardboard on the outside. That would make it much easier to seal a weather balloon to the tube as well, because silicone and pretty much anything else sticks to HDPE pretty well, and it can be drilled and screwed easily too. The sonotubing is too weak for that and it is hard to get anything like silicone to stick well to that polymerized (or wax) inner coating.

    I assume that since something like a weather balloon can hold helium, that it will not allow CO2 to diffuse through it over time, would I be correct in that assumption?

    I am thinking it would be a good idea to add a simple oxygen level sensor to the room as well. That way I can instantly know if the oxygen levels are adequate, since the oxygen level in the sealed room will most likely determine the equilibrium oxygen concentration the fish will have in the tanks at night. That would better help me to know when it might be necessary to flush the room and restart the system with fresh air due to low oxygen levels. I am thinking that if the room ever did have any sort of a leak to the outside anywhere, the CO2 would always be replaced from the CO2 tank, but the oxygen wouldn't because the room would most likely always have a slight positive pressure just from the CO2 tanks letting out CO2 periodically. That would mean that oxygen levels could theoretically drop over time and just monitoring the CO2 wouldn't give me all the info I would need to know that the fish and I were safe in that environment. Having a simple oxygen sensor would allow me to keep tabs on that easily.

    From what I have been reading, most of the effects caused by the middle range levels of acceptable CO2 (which is the 1-2.5% range of CO2 in air I am concerned with) are more a result of lowered oxygen levels than elevated CO2 levels. Higher levels of CO2 usually only happen in crowded rooms or areas where lots of people are using the oxygen and adding to the CO2 at the same time. If I did find a boost in tank room oxygen levels just from all the net oxygen production from the plant tanks I would think that any of the common effects from elevated CO2 levels (like heavier or faster breathing in order to expel the CO2 and acquire the O2 needed) would be lessened to some extent by also having higher than normal oxygen levels.

    I really like that pressure equalizer idea Vaughn. I just realized that it would solve another problem I was thinking about as well. I was trying to figure out if the room was sealed, and the CO2 was being pumped in over time (especially when first being reset after a room flush with fresh air and the room instantly then getting a 1-2% increase in gas volume to reset CO2 levels) if the increase in pressure would be enough to blow bubbles of good CO2 air through the p-trap of the tank room sink drain, or a floor drain, and into the sewer. I was thinking I might need to make deeper p-traps that would take more of a pressure change before letting any gas through the drain lines. Now with the equalizing balloon the pressure would always be exactly the same as outside, so I would never be losing CO2 air or pulling in sewer air (to balance out a pressure difference) through any plumbing drain anywhere, so I should be able to just use standard p-traps on the plumbing drain lines.

    Have a good one, Jeremy
     
  14. VaughnH

    VaughnH Lifetime Charter Member
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    That is good reasoning about the p-traps. They normally only hold about 4-6 inches of water, so a half inch Hg pressure increase in the room (about 6" of water) would push the trap water out.

    But, you are wrong about HDPE, which is a "release agent" for almost all adhesives and resins. Virtually nothing sticks to polyethylene. I think for this to work, you need a very slack thin membrane of rubber as the balloon, and it would have to be mechanically captured and sealed between two lengths of sonotube.

    I keep thinking there has to be a better way to use this idea, other than filling the room with high CO2. For example, an acrylic box with an aquarium inside, with a removable, but sealed top on it, for maintenance access. Perhaps a coffin size box that holds three aquariums, or something along that line. I'm nervous about the safety hazards of a CO2 filled room. Perhaps a room with aquariums in the wall, with the back side being a room having the high CO2, but sealed from the viewing side.
     
  15. jeremy v

    jeremy v Guru Class Expert

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    Vaughn,

    You are right Vaughn. I looked it up and found the same thing. That is interesting, because I have actually done this in the past and it worked fine. It was several years ago, but I remember sanding the two surfaces heavily to roughen them up and then laying down silicone and sandwiching it between another piece of HDPE and then screwing the two pieces together tightly. I guess now that I think about it I didn't actually make a bond between the silicone and the HDPE, I just used the silicone to make a "mechanical gasket" that was actually held in place by the pressure of the two pieces being screwed together, so that must be why it worked. I guess I just assumed that the bond held, but in actuality it didn't and in that application it never mattered because the mechanical pinching effect creating the gasket type of seal still covered me. Thanks for letting me know.

    I have been trying to think of a better way to do this as well so I wouldn't have to fill the whole room with CO2. My best idea so far would be to have a large acrylic "bell diffusor" for lack of a better term over 75% or so of the filter tank water surface area. Then I could just leave the bell on there at all times because the mechanical filter pads would be in the other 25% of the filter. Pipe them all together as one and have them directly attached to the CO2 tank via a solenoid. Then I would have a much smaller air volume to deal with, and if the bell covered 25% of the total tank and filter surface area (for instance) I would inject the CO2 into the bell chambers to 4x the necessary concentration to give a 30ppm equilibrium with the water. I am thinking that having 25% of the water surface at 100,000ppm of CO2 would be about equivalent to 100% of the water surface at 25,000ppm if outgassing from the rest of the water surface was kept to a reasonably low level. Then I could have an air pump that pulled high CO2 air from within the bells and sent it through airstones that put the air into the water under the bell so that the high CO2 air diffused easily into the water and whatever floated to the surface of the tank water still remained trapped in the "Bell" system. Then I would have regular full access to the tanks and I could have regular tank room doors, air, etc. and no sealed areas necessary within the tank room itself. That air pump would need to be able to handle very moist air though since it would be constantly recycling the same humid air, and it would also need to be able to handle the acidic CO2 air over time without excessive pump damage as well. I don't know if that's possible. That would be the key to this working, because without it I don't know if the CO2 would diffuse into the water fast enough to stay consistent within the tank water. That setup would allow me to still have the increased accuracy of the air CO2 controller and I could still have only one controller to keep tabs on most of the time once everything was working fine and testing to the right levels via a pH probe in the tanks initially to tell me I was getting sufficient diffusion of CO2 into the tanks.

    I am starting to think the whole room idea is going to be more hassle than I am wanting as well. If I was going to build a large tank room and have lots of tanks and grow aquatic plants to sell for a business, I would most likely go ahead with at least trying this (starting with low light plants and lower levels of CO2), but I am thinking that it would be much easier to have a few less tanks and have each tank be a little larger so that I can have the same volume of total water to work with and grow plants in. Then I would have greater stability in the tanks and less total tanks to monitor and provide bubble counters, reactors, etc. for.

    That is actually what I am wanting and what I was already picturing. To have the 3-4 main display tanks viewable from outside the room (through the walls of the tank room) from the living areas of the home. The tank room itself is basically only for maintenance, water changes, cleaning, the filters, and deadening the noise of all that stuff and that's it. Viewing the tanks would be done from the other rooms of the home and that would just be regular air for breathing. There will be no viewing going on from the tank room, because you will only be able to see the backs of all the tanks from in there and that's it.

    What is complicating everything the most in my mind is how I would be able to make the tanks viewable from outside the room on three of the four walls and also keep the room sealed. I want the tanks to just look like in-wall tanks from the living areas of the house. I would also really prefer to not have to do my aquascaping and all of my maintenance from behind the tank looking down into the top of the tank water, haha. That seems like a huge hassle, especially for accurate plant trimming. If I make some little cupboard doors above the tanks in the walls I would have to seal them really well and I would lose most (or all) of my CO2 if they remained open for while when doing tank maintenance.

    My best idea so far (related to still filling the whole tank room with higher CO2 levels and giving me easy access to the tanks for maintenance without losing my CO2) is to install double pane vinyl windows that are the exact same size as the front aquarium glass in the walls of the fish room (for the viewing windows) and then having the tanks pushed up right against the vinyl windows so you could easily see them from outside the room and the room remained sealed airtight. I would have to keep humidity in check to prevent condensation on the glass. Then having each of the tanks on custom heavy duty stands that I could build which would have a fixed pivot off of one corner (and heavy duty fixed casters on the other corners) so I could rotate the entire tank and stand 90 degrees into the tank room. Then I could do all of my maintenance on the display tanks from within the tank room and I could easily see what I was doing from all sides (for aquascaping and plant trimming) while also not letting any CO2 out of the room. Then when I was done I would just slowly rotate the tank back flush against the vinyl viewing window. I could make it so that all of the tanks pivoted into the same space in the center of the room so no space was wasted, and I would just pivot and clean or work on one tank at a time that way.

    Have a good one, Jeremy
     
  16. VaughnH

    VaughnH Lifetime Charter Member
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    Another problem is that just having a high CO2 concentration in the room air doesn't mean the water uniformly has a 30 ppm concentration. Remember, the plants will be consuming the CO2 in the water, so the lower levels of water will become depleted of CO2 to some extent, unless you have the same good water circulation that is needed with current CO2 systems. This makes me wonder if there really are advantages to the high CO2 room air method.

    One picture that keeps coming to my mind is tanks having drilled bottoms, so all penetrations into the tank come from below. Nothing from above. Then you top each tank with a sealed canopy, maybe something like an acrylic dome over the tank, but sealed all the way around, so no gases can escape. Now, increase the CO2 concentration in that canopy to the 30,000 ppm or so that you are talking about. If the under-tank plumbing/pumps will create enough water circulation this could be enough to keep the water at 30 ppm. But, is this a better method?
     
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