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CO2 Injection Methods - pros and cons

Discussion in 'CO2 Enrichment' started by scottward, May 26, 2009.

  1. scottward

    scottward Guru Class Expert

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    Hope this hasn't already been done....I couldn't find it using the 'Search'... :)

    Let's do up a table here - all the different ways of getting CO2 into the water with the pro's and con's of each.

    The table then could be sorted in order of efficiency.

    I could help put the table together, but input from the gurus would be required.

    And let's assume that it applies to proper pressurised CO2, not DIY (i.e. soft drink bottles filled with yeast and sugar).

    So, starting with the different ways of getting the CO2 into the water, in no specific order yet, and we can do the pros/cons afterwards...

    * Airstone placed on the bottom of the tank
    Pros: Easy, cheap, quiet.
    Cons: Airstone can clog up over time. Would need to be coupled with decent circulation to get some kind of stability? Largish air bubbles - not the best surface area?

    * CO2 tubing connected to intake of canister filter
    Pros: Easy.
    Cons: Can make filter noisy. Causes CO2 instability as the filter starts to clog up the CO2 is obviously affected. Canister filter alone would not provide enough circulation unless grossly oversized for tank capacity?

    * CO2 tubing connected to intake of a powerhead (unmodified)
    Pros: Easy, relatively cheap. Intake strainer easy to keep clean on a daily basis so that the flow rate stays consistent. Best way of getting good circulation?
    Cons: Noisy. Bubbles all over the tank unsightly for some people.

    * CO2 tubing connected to intake of a powerhead (modified - snipped and 'furred' up)
    Pros: As above - but this time bubbles coming out are smaller, therefore have larger collective surface area and rise to the top more slowly thus an increase in water contact time.
    Cons: Requires manual modification of powerhead impellor (risk of breaking it or otherwise stuffing it up I guess). Maybe a bit quieter with smaller bubbles but I'm sure it still wouldn't be silent? Bubbles all over the tank, unsightly for some.

    * ceramic disk
    I don't know much about these - they can clog easily though I think?

    * external reactor (e.g. AM1000?)
    I don't know much about these either. First though is that they are $$$.

    * 'ladder' type internal reactor
    Haven't used one of these - large and unsightly in the tank? Maybe $$$?

    * CO2 bell
    Pros: Cheap, easy, quiet.
    Cons: Unsightly? Lots of small bubbles is going to provide much more surface area than one large bubble trapped inside a 'bell'.

    Hey this is only a first draft - but with some refinement this could be a pretty useful table for us?

    Scott.
     
  2. Philosophos

    Philosophos Lifetime Charter Member
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    I've only used disks, so I'll keep to what I've experienced directly.

    Disks offer nothing of distribution on their own. You have to use the outlet to blow over them, or have strong current in the area. They need weekly cleaning. If I'd known, I'd have ordered a dozen disks, and just done bulk cleanings every now and then. They're usually cheap unless you buy ADA, in which case you're paying for the brand.

    -Philosophos
     
  3. scottward

    scottward Guru Class Expert

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    Hi Philosophos,

    Cool, thanks for the info.

    I'll wait until other people have added some input, then I'll compile a 'second draft'.

    Scott.
     
  4. shoggoth43

    shoggoth43 Lifetime Charter Member
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    Efficiency for dissolving CO2:

    Airstone : Low

    Ladder : better, but still low

    Diffuser disk : better than airstone/ladder, but still on the low side.

    Impeller chopping : med/high

    Reactor / Cannister : high since you can dissolve nearly all of the CO2


    NOTE: dissolving CO2 is not nearly the whole story. Flow is critical with CO2. If you aren't distributing the CO2 well, then it's pointless. You also have the misting methods using the impeller chopping. This is theorized to give plants direct "emmersed" access to the CO2 but other factors may be at play. It's also likely the the misting effect usually more efficient than it would seem because the way to get the mist is to use a Mazzei type injector or powerhead, which gives more flow. Surface agitation also plays a role. Too much and you just dissipate the CO2 into the air. Too little and you can cause other issues with either surface scum, or just not enough turnover to allow adequate O2 into the water.

    -
    S
     
  5. Philosophos

    Philosophos Lifetime Charter Member
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    The diffusion rate is higher for reactors, but Tom was saying in a couple places that isn't necessarily better than bubble mists. Maybe we could get his commentary as to why and how?

    -Philosophos
     
  6. cggorman

    cggorman Prolific Poster

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    I'm using an AM1000 inline with my canister. It's amazingly efficient. with a Ph controller and running 20-30ppm, a 5lb cylinder lasts at LEAST 6 months. 2 bubbles/sec is enough to keep me on target. There is no noise or visible bubbles anywhere.

    I've never checked distribution asuming that it was as even as possible given apparent 100% absorption and good water circulation. Perhaps I should move my drop checker around to see what's going on....

    It was an expensive setup, though I feel the setup cost was balanced well with the lack of in-tank clutter, control, and long-term CO2 savings.
     
  7. fjf888

    fjf888 Guru Class Expert

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    This is a nice little discussion going. On my tank, which is a reef ready with sump, I built the reactor as described here and run the CO2 into the impeller of my pump and from there and from the outflow of the pump into the tank. I waste CO2 due to the sump setup, but with 600gph circulation on my 72G I get very good coverage, the drop checker is consistently lime green colored no matter where its placed. So I agree with the above that probably flow is much more important that many realize.

    The setup I am working with is a 72G with a Eheim 2028 Filter and no sump. Perhaps the AM 1000 would be the way to go.

    I know I need CO2 now. Already getting green spot algae on the above tank after just two weeks, along with the std diatoms.
     
  8. Gerryd

    Gerryd Plant Guru Team
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    Hi,

    A couple of thoughts.......

    I know Tom replaced his mazzei venturi with discs recently and reported that the performance is about equal. Am looking for the thread now.......was recent.

    So, I think the efficiency of the disk should be rated higher, as I think a venturi is very efficient at c02 dissolving/mixing.

    Discs do need to be cleaned often and it seems from reading threads that this is not always the case and that some folk do not realize how clogged they can become.

    Also want to note that HOW the component is used/configured will affect it's efficiency rating. An underpowered/undersized reactor will not perform optimally.
    As pointed out, a disc needs an additional source of current for distribution.

    The needle wheel approach also seems to be pretty good.

    I now use a mazzei venturi, but have used reactors in the past.

    Really depends on many factors, so is hard to grade each method consistently/fairly unless we use some control tanks like Tom does and try each method and compare.

    A disc on a 10 gallon with good current may be more effiicient than a mazzei in a 120 gallon with sub optimal flow........
     
  9. PMD

    PMD Lifetime Charter Member
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    For reactor users I would like to emphasize CO2 circulation and distribution. It's imperative that the dissolved CO2 is:

    Adequately circulated and
    Equitably distributed.

    Ideal circulation can be achieved with a dedicated separate pump that would in my estimation have a gallon per hour rate of seven or more times the gallon size of the aquarium.

    Ideal distribution can be achieved with a dedicated spray bar attached to the separate pump described above. An ideal spray bar would extend the length of the aquarium, sit on the substrate in the back of the aquarium since CO2 naturally flows upward and have forward facing very small holes every two inches or so for distributing the CO2 enriched water.

    For example for my standard size 125 gallon I have the following:

    A dedicated Ehiem 1262 (900 GPH) pump connected to a 3" diameter 24" long PVC reactor connected to a 1/2" diameter PVC spray bar that extends for six feet and resides in the back of the aquarium on the substrate.

    Regards,

    PMD
     
  10. mi5haha

    mi5haha Prolific Poster

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    I think Tom Barr mentioned that mist Co2 breaking this "boundary layer" is the key for better result by misting Co2. This layer is said actually a layer of water staying on the surface of leaves without much movement, thus preventing other water carrying even 100% dissolved Co2 touching the leave surface.

    Co2 in mist can break this boundary layer, thus leaves can absorb Co2 more efficiently, so pearling by mist way can be observed in the first hour when the light is on.

    Disc needs water circulation to assist Co2 distribution. Powerhead misting itself can creat circulation by its own.
     
  11. Tom Barr

    Tom Barr Founder
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    Well, equal with some adjustment and more CO2 bubbles/per sec etc....you can get the same result but with more fiddling and more CO2 usage.

    Using the mist methods, needle or mazzei, it's easier, more stable(if you clean the filter if you use in line post mazzei) and you use less CO2.

    The tanks are the same tanks with the other factors being pretty equal and the plants/algae being the gauge, I give the method a few months for each and tweak and give them all a fair shake.

    Each method of CO2 should, at least in theory and practical use, be able to produce a decent nice result using CO2..........

    You might have to fiddle more, or adjust or clean more often, use more CO2 to do it.........but they all should do essentially the same thing.

    Regards,
    Tom Barr
     
  12. Gerryd

    Gerryd Plant Guru Team
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    Hi,

    This is a common assumption with unfortunately almost no evidence to support it, considering the lack of common/inexpensive tools to measure c02...I was under this same spell for a while till Tom broke it for me :)

    I would definitely advise moving the checker around.......flow in the tank is vital and Tom has shown (with an expensive c02 meter) that the ppm value changes from minute to minute and area to area even within the same plant groupings.

    Also, please remember that checkers are not that accurate and reflect what the conditions of the tank WERE, not necessarily what they are NOW......

    Is like looking at starlight, you see it now, but was generated many light years earlier......not sure if that is a good analogy.....

    I worked on my outlets and flow for weeks and kept moving the DC around the tank looking for weak spots........I still am not 'sure' but do feel better about it.

    If you see all plants getting flow, this is a good start...

    If good growth and no algae, you are doing it right......



    Tom,

    Yes, I meant that with some adjustment and fiddling, but should have been more clear. I gave the impression that it was plug and play and no more..

    Still, equaling performance between discs and a mazzei can be done, and that is an important point, when we think we HAVE TO diffuse a certain way based on tank size alone........
     
  13. scottward

    scottward Guru Class Expert

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    Just waking up an old thread here...

    This idea of running a spray bar along the back bottom of the tank sounds to me like the absolute *best* way of distributing the CO2.

    PMD - how long has your tank been up and running and what are your results like?

    Scott.
     
  14. PMD

    PMD Lifetime Charter Member
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    Scott,

    The tank has been running since July 2008 and I am satisfied with the CO2 dispersion.

    No bubbles are noticeable exiting the spray bar holes which indicates to me that all of the CO2 is dissolving in the reactor.

    Pearling generally occurs an hour two after the lights turn on and pearl the remainder of the day.

    I probably could have a used a more powerful dedicated CO2 circulation pump than the Eheim. It's adequate but a more powerful pump that could be slowed down if necessary may have been better.

    Make sure that the spray bar holes are very small and directed slightly upward to minimize substrate movement. If the holes are too small you can always enlarge their diameter. Mine are 1/32 or 1/16 of an inch.

    I do have some minor BBBA infestations on the plants near the top of the aquarium. I believe this to be the result of my lights which sit directly on the aquarium. I plan on acquiring stronger lights in the future and suspending them a foot or two over the aquarium. This should result in contracting the range of the light strength between the top and bottom of the aquarium and hopefully resolving this minor issue.

    Besides the dedicated Eheim, I run two aquaclear HOB 500 GPH filters for additional circulation and a Magnum 250 for water polishing. They turn off via timer when the CO2 and lights are on to minimize the CO2 from escaping. I noticed a problem when they ran concurrent with the lights. Two powerheads round out the circulation pumps.

    I also run two Eheim 2217 filters filled with filter floss that are cleaned once every three months.

    Regards,

    PMD
     
  15. scottward

    scottward Guru Class Expert

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    Hi PMD,

    Thanks for getting back to me.

    Glad to hear that this technique of dispersing the CO2 enriched water is working for you.

    I'm thinking of doing something similar - except perhaps I might run my spray bar, at substrate level, along the mid line of the substrate rather than at the back of the tank, and I might drill the holes in an opposing way such that some point slightly towards the front of the tank and some to the back.

    I could paint the spray bar the same colour as my substrate so that it doesn't stand out too much.

    As far as distribution goes, as long as it's coupled with an adequate pump to ensure that the small jets of water are all relatively equal along the entire length and some general circulation powerheads, I really can't think of any better way to distribute the CO2 evenly??

    Does anybody have any other thoughts on this? This technique must be the best going?

    Scott.
     
  16. PMD

    PMD Lifetime Charter Member
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    Much thanks to VaughnH, Gerryd, and ceg4048.

    They put me on the right track a year ago!

    Regards,

    PMD
     
  17. VaughnH

    VaughnH Lifetime Charter Member
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    I am using a reverse flow undergravel filter to distribute CO2 enriched water from an external reactor - simple DIY type. That has to be the most uniform method available for distributing CO2 evenly all over the tank. But, it doesn't stop BBA entirely. There doesn't seem to be a magic bullet for stopping BBA entirely.

    I have been very pleased with the RFUG, mostly because my tank water is always very crystal clear now, but also because this is a maintenance free method for diffusing CO2 into the tank. Nothing to clean every week, no soaking in bleach, no scrubbing, etc. I'm not yet convinced this grows plants as well as other methods, but it does grow them.
     
  18. scottward

    scottward Guru Class Expert

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    I was thinking about something like this as well - but I was thinking that a UG plate with so many slots in it would mean that you would have more CO2 coming out closer to the inlet which would taper off the further you go from the inlet?

    I'm thinking that a higher pressure spray bar would probably actually give a better result, as the amount of water coming out of each hole would be more equal.

    Scott.
     
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