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Turning off CO2 at night, could someone explain this to me?

Discussion in 'CO2 Enrichment' started by sayhy2mark33, Nov 23, 2007.

  1. VaughnH

    VaughnH Lifetime Charter Member
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    The water in a planted tank is not likely to contain only CO2 and carbonates as things that affect the pH and KH. The water likely does contain phosphates and tannins, and that means the relationship between pH, KH and ppm of CO2 is no longer valid. Even if you don't add phosphates to the water, tap water usually contains phosphates added to raise the pH above 7.

    The 1.0 rise in pH method doesn't work because we have no easy way to determine how much CO2 is in the "degassed" water. If you do some experimenting you will find that the tank water pH will continue to rise for at least a couple of days when you let it sit out in the open air. Even after it stops rising, unless you find a way to measure the ppm of CO2 now in the water, you still don't know how much is present. All that the 1.0 rise in pH test tells you is that the ratio between ppm of CO2 in the tank and in a "degassed" sample of tank water is 10. Without knowing the degassed ppm of CO2 you can't find out from that what the tank ppm is. We used to assume that a degassed sample would have about 3 ppm of CO2 in it, but that is a bad assumption.

    You can check this yourself, with some effort. Get some distilled water, add enough baking soda to get a KH of something like .5 dKH. Then use a straw to blow in the water and get some more ppm of CO2 dissolved in it. Now, use a pH probe to measure the pH of the water over a two day period. The equation relating ppm CO2 to pH and KH will be correct for that water, so you can calculate what the ppm of CO2 is at any time. If your results are similar to mine, that number will be as low as .5 ppm if you wait long enough.

    Only the drop checker method gives "accurate" results, unless you spend a lot of money on laboratory equipment.
     
  2. Crazy Loaches

    Crazy Loaches Guru Class Expert

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    Yeah I am aware the ph/kh chart will most likely not be valid (I never suggest using such a chart on plain tankwater), due to other pH effecting acids/buffers, which is why I mentioned the method that involves only the change of co2, meaning co2 is changing but others acids/buffers probably are not. And yes, I did say the method relies on you having 3ppm co2 after degassing. So the issue with this method then is your saying tank water often does not hold close to 3ppm upon sitting out for a few days (or before the addition of any co2)? So far on my 75g tank my 1* rise after degas has corresponded to green on my DC, but I understand this might not be the same for everyone. But remember a DC isnt perfectly accurate either, unless your using lab grade KH reference fluid and have a darn good eye for what shade of green 6.6*pH is (to me +/- .1* isnt discernable, and less than a .15* difference is already off by 10ppm).

    That sounds like an excellent test. I will definitely do some experimenting along those lines to see just how much the co2 is at equilibrium. I have a good amount of surface movement in my aquarium also, which could effect those readings, so I might place a powerhead in a small clean container and do the test with that just to see if it has any effect.
     
  3. Crazy Loaches

    Crazy Loaches Guru Class Expert

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    Tom... question for you (or others opinions welcome also)...

    Seems like your a big proponent of shutting the co2 off at night. I do this currently, but my new tank I am setting up with a pH controller and debating what to do along the lines of co2. How did you setup the behemoth? I remember seeing you used an AC3 Pro, which is also why I ask because I am going to be using an AC3. I don’t know how fast my water will degas or how fast the co2 can come up, haven’t done any testing on it yet. It does have a lot of surface movement due to the overflows, and a lot of churning down the Durso's. Using a 3600gph Sequence Dart pump turned down slightly (will determine actual flow rate soon).

    It wouldn’t be to hard to program the AC3 to shut off the co2 at night, is that what you did? I am just not sure if my tank degasses really quick if its a good idea to have such a large swing? With some custom programming it is possible to have the AC3 target a different pH value at night. For example I could set it up so that it controls to 30ppm during day, and say 20ppm overnight. Or would you just shut the co2 down entirely overnight?
     
  4. Crazy Loaches

    Crazy Loaches Guru Class Expert

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    Just bump'n it to see if anyone has any more thoughts on my question above... Basically if it is possible to target a lower co2 concentration at night would you do that or still shut it completely off so long as it could still come back up to 30ppm in a reasonable amount of time?

    For example, in my tank I am about to start up with a controller, I have it set for 1hr prior to lights on to control to 6.4 (estimated 30ppm) through lights off, and all other times to control to 6.65 (estimated 17ppm). I havent done thorough testing yet or checked with a DC so those numbers may change.
     
  5. detlef

    detlef Member

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    Let me add a little side note here on how to properly set the starting time for CO2 delivery in the morning. This is even more important since we know plants really take off growing intense during the early times of light. Sorry if this topic has been covered before but I think it's very important having set the CO2 system right especially at the beginning of the photoperiod.

    Use the pH probe or any kit for pH testing to check at what time decent CO2 amounts are actually reached. Because of their long lag time (2-4 hrs) drop checkers are not at all useful to test for the CO2 amount at a particular time.

    So when you see the color of the drop checker being greenish (filled with 4dKH water of course) as it should be indicating 20-30ppm CO2 wait about 3 hrs and then test for the pH. This same pH should be reached at the time the lights come on. I have set my CO2 delivery system to start 3hrs!!! before lights on and I really do not think mine is very slow or underpowered.
    And no I don't have fish gasping for air early in the morning.

    Best regards,
    Detlef
     
  6. Tom Barr

    Tom Barr Founder
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    We can always hear this topic again and again and again:)
    Even myself:D

    I think this is the most critical time period myself also.
    If CO2 is good at that first 5 hours, things seem to do quite well.
    Even if you allow it to taper off later...........

    3 hours will give you plenty of lag time!
    But .......good measurement.

    In general, the smaller the aquarium, the easier it is to have a pH controller system. The larger systems have lag response issues. You can drive things faster/better with more flow, but the system is a lot more complex as far as flow and local areas that high flow vs others that are low flow, adding plants and rocks and wood, makes this even more complex.

    The other issue is the control function, it's not really a control of pH, it's only as good as the delivery system you have for CO2, that means you need a good delivery method if you want to use it.

    I have AC3's, but I do not use them for their control functions, never have.

    Some have used them to shut off the lower range pH's just in case, and left the range of pH really wide, say that you are pretty sure a pH of 6.1 is your fishes' limits.

    You can set the shut off of the solenoid at 6.2.
    Typically, the tank runs at 6.3 pH and you get good growth and good fish health.

    And you set the upper ranges the same way.

    But I would rather just dial in the CO2 amount with a needle valve, then I know it's very stable.

    When the lights come on, I have high flow running through CO2 delivery ,method, so the CO2 ppm's are achieved fast, I can also turn the CO2 on 1 to a 1/2 hour before the lights come on.

    That way I have pretty good CO2, no control function that might fail etc.


    I do not need to calibrate the needle valve, it is always stable. I do need to calibrate the pH probe............
    I also do not need to calibrate a timer, or the solenoid.................

    So it makes it more redundant and safe to set it up this way vs the pH controller method.

    I think pH controllers and high light are very similar, folks think "more" is better..........

    It's not, it's just more work.
    Amano does not like pH controllers either for many of the same reasons, I asked him.

    Clients often like all sorts of bells and whistles............so you try and modify them to get around their desire for gadgets.

    Generally, they stop using them or never learn how to use them with all the programming etc anyway....so they end up being a 200-3000$ piece of unused equipment:) That's what I tell new clients thinking about getting one.

    Generally deters them.

    AC3's have other functions, data logging of pH, Redox, O2, temp, conductivity, nice timer controls of the lighting, dosing pumps etc.

    For monitoring and timers, this makes things much easier to spot trends etc and you can add more/less via needle valve and see the results.

    CO2/pH etc are secondary considerations, we really want to know two things:
    good plant health and growth via pearling, nice growth and good fish health.

    What is the optimal balance there?
    That's really a fuzzy thing because folks have different opinions about what that optimality is.

    For some, having 2 w/gal and less/leaner gives them their ideal.
    Others want more light and more CO2, more nutrients.

    Both work, as do gradations in between.
    By pushing the limits of each parameter(eg adding a lot more light+ CO2), I can make a system more sensitive to changes.

    Then I can use that data to suggest an ideal range that works well and has the most wiggle room. But careful, make sure you know what it is that you are really testing(the plants and fish or the nutrients/CO2) and be able to provide a control consistently (a nice example of the growth you want)

    Regards,
    Tom Barr
     
  7. Crazy Loaches

    Crazy Loaches Guru Class Expert

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    So Tom, sounds like you are pretty much against controllers then for co2. I've never used them yet, but upon making the decision to automate everything it was just something easy to do to setup co2 to control via the pH. Its really no big deal to me, and I could always just set it on a timer control instead of pH control, except... I am rather disappointed in the needle valves I got. And I got a whole bunch of them with the intentions of setting up a centralized whole house co2 system. They (clippard) even screwed up and sent me a few extra that werent on my order. I've been running the co2 now for about a week and noticed they do not hold a consistent bubble count. I thought thankfully since I am using a controller this shouldnt be a big deal as long as I set the initial count pretty high. So if I want to ditch the pH as the control then I am going to have to be getting some better needle valves, which I may do. I suppose in the meantime I will still use the controller though. I'll try a different pair of needle valves though, just in case the first two I grabbed are just less accurate. The clippard check valves also take a little bit of pressure to open, I wonder if they could be causing the inconsistency.
     
  8. Tom Barr

    Tom Barr Founder
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    Yes, but they do make excellent monitoring devices for data collection, better the pH monitor to take readings every 15-30 minutes for 2 months for me to look at rather than having to stay up all night for 60 days taking readings:)

    The idea that using a needle valve and bubble counter/mass flow meter to measure and add CO2 is wiser. It's simpler, does not have the issues of pH/KH problems, measurement etc, does not rely on dose lag time responses etc.
    No programming required either, WHAT HAPPENS IF THE Ph PROBE FAILS/MOVES AROUND, FALLS OUT ETC? Solenoid sticks from bouncing back and forth from opening/closing too often? A solenoid can turn on off so many times, so once a day is fine and all we need anyway.
    I just think it's a safer way to set things up and has you focus more on what matters most: plants and fish, not a set rigid pH point.
    A pH set point is fine once you find a a good range and are fairly confident of it, but tap changes and that might change the pH also.

    So things can still fool you.
    Eyes seem the best method to test.

    Well, if you make a large centralized set up, then other issues besides the valves are becoming a problem. Using metal gas line tubing and placing the needle valves at each point of entry is likely a better/best option. Then you only have many 1 meter of soft CO2 tubing till you add the gas to the tank, also makes adjustments much easier on each tank.

    Then you run the gas pressure at about 20psi in the metal line.
    If you try to do this at low pressure, say 2 psi, the time it takes and the poor low pressure+ using soft line will stretch and cause issues with stability, the softer line is designed namely for low pressures, not 10-20psi etc for large arrays of multiple valves.

    There are quite a few valves out there, but they cost more.
    I like some automation, but generally am against it.
    I do like monitoring and automation there.

    If something screws up there, I just lose data, not the plants/fish etc.
    I look at these things as devices to save me time/labor, not add to it.

    Given the vast array of variables, I trust my own eyes, and like things that are easy to adjust and do not move after I do adjust them.

    I like water changes that involve a pair of valves, one to drain, another to fill vs totally automated water changers.

    I like timers for lights, there are some things that are easier to rationalize.........but pH control ain't one of them for me.

    Hybrid use of pH control, to set cut off at lower pH's (gasping fish levels)ought to be fine though.
     
  9. Carissa

    Carissa Guru Class Expert

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    Here's what I come back to with this subject... testing distilled offgassed water should tell you how much co2 you have at atmospheric equilibrium. Just test it and use the co2 formula to determine it. Then test your tank water and let it offgas. I can't see any reason why the amount of dissolved co2 from one water sample to the next, sitting right next to each other, would be any different, given enough time to come to equilibrium with the atmosphere. Then you will know exactly how much ppm of co2 you are ending off with, and from this you can easily calculate what you started with. The only difficulty with this is the error/inaccuracy in reading the color if you are using a drop test, and if the amount of co2 in the atmosphere changed dramatically within the amount of time you allow the samples to come to equilibrium it would mess up results.
     
  10. VaughnH

    VaughnH Lifetime Charter Member
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    You can stick a straw into a glass of water and blow a few bubbles, then the water will have up to 10 ppm of CO2 in it. So, I wonder if just breathing near an open water sample will affect the amount of CO2 in it. I didn't try to test that, but it wouldn't be hard to do.

    If you were to set up 5 containers of known low KH distilled water side by side, wait some time, such as 8 hours, then measure the pH of each container, you would be able to see if all of them reached the same ppm of CO2. Now, repeat this a few times with different room temperature, room heat on then off, windows open, then closed, etc. and see how much the 8 hour ppm varies. If all goes well all of those samples will have something like 3-5 ppm of CO2, with a spread of less than +/- 1 ppm. You could then use this as the standard equilibrium ppm of CO2 for your location, and use the change in pH from in tank water to 8 hours sitting in the open water, and from that tell how much CO2 is in the tank. To be accurate you would have to be using a pH probe, not a titration test kit.

    Obviously this takes a lot of work to determine that the method works with reasonable accuracy, and worse, the time lag to get a reading would be 8 hours vs. the 2 hour or so with a drop checker.
     
  11. Carissa

    Carissa Guru Class Expert

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    Since there are no outside variables in the known KH water, the CO2 formula is accurate in determining the exact ppm of co2 at any given time no matter what it's at equilibrium with (within a small margin of error).

    The only thing that would matter would be that you can accurately measure pH in tank and known KH water samples, and that they come to equilibrium with each other. Whether they come to 3 or 5 or 10ppm doesn't really matter as long as they are the same. As long as they are both subject to identical conditions for a long enough period of time...I can't really think of any reasons why two samples of water sitting next to each other in the same type of container exposed to the same atmospheric conditions under nearly identical conditions would not reach equilibrium with each other. Isn't this the whole premise of the drop checker?

    The question would then be how long does it take. I would think that since it takes a couple of hours or up to 4 hours for a drop checker to reach equilibrium with the tank water, it would take about the same amount of time going the other way, for tank water and known KH water to come to equilibrium with each other assuming you use the same quantities of each as you would use in your drop checker. Initial testing could be done just to see exactly when the pH stops changing or is changing in both solutions at the same rate which would indicate equilibrium.

    Obviously if someone has a drop checker this wouldn't usually be needed, but I'm just saying as an alternative method it would be as accurate as a drop checker, or actually even more accurate if you use a pH probe, with a little more hassle involved. With use of a pH probe it should be possible to determine with very close accuracy the exact ppm of co2 you started with. With drop tests the accuracy would depend on how close you can read the test. If someone was concerned about whether the solutions actually come to equlibrium with each other, you could use two or three samples of each, the known KH and the tank water and test them all to see if there are a range of values or not. In a sense, you would be building a type of reverse drop checker, if you know the exact ppm of where you ended, and you know the difference in pH between where you started and ended, you know the co2 you started with.
     
  12. VaughnH

    VaughnH Lifetime Charter Member
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    No equation gives an exactly correct answer. The accuracy always depends on how accurately you make the measurements involved. And, because the calculated ppm of CO2 in water is proportional to 1 divided by 10 raised to the pH power, a small error in pH means a big error in ppm of CO2. That's why the drop checker, using visual judgment of the color, can never be more accurate (at 30 ppm)than 25 to 40 ppm. Using a calibrated pH probe. that is accurate to .1 pH, instead of visually judging the color, is a lot more accurate, but it still only gives a 10% accuracy. And, all of this assumes you know the KH very accurately. But, our test kits for KH are only good to about .25 dKH at best, so that adds another 6% or more error.

    Fortunately, we don't need to know the exact ppm of CO2 in the tank. Knowing it is more than 20 and less than 40 is good enough for what we need it for. Less than perfect water circulation may give a bigger inaccuracy at any given point in the tank.
     
  13. Carissa

    Carissa Guru Class Expert

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    Yes, the obvious limitation for any of this is the lack of precision testing equipment. If someone wanted to spend a lot of time and effort they could probably get within 5ppm for sure (testing multiple samples for pH to eliminate error that way, and watering down the KH test kit to account for a 2.5ppm change in KH or something small like that). It isn't really useful to anyone to do this unless they don't have a drop checker, in which case it is at least a second option that will provide some measure of accuracy at least to the degree that we need to have.

    As far as circulation, this seems to be a hot topic but with a lot of unanswered questions out there. It is always presented as a possibility when things go wrong, but at least for myself, I've never seen any evidence that a lack of co2 due to poor circulation is a factor large enough to be reckoned with in most normal circumstances. Wouldn't this be easily tested by using a pH probe to determine if the pH is different from one portion of water to another, thus showing a variability in co2 readings in those spots? If the changes in co2 concentrations are significant enough to be affecting the tank, wouldn't it be easily measurable? Has someone just not done this? Or are there other factors I'm not thinking about?
     
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