Re: [APD] CO2 and pH control

[Gordon and Susan Watkins <gwatkins at ritternet_com>]

David,
    I really appreciate your taking the time to provide such a thorough 
response to my question.

    Yes, you are correct in assuming that this was once a reef tank. And 
you're also correct that my filtration system is probably overkill for a 
29 gallon tank, but I like to tinker - what can I say? The filter is a 
modified RDP filter with a bioball tower added (no current RDP 
fiunction) There is a 3 gallon glass chamber filled with Dupla bioballs 
beneath a perforated drip plate covered with poly fibre quilt batting as 
a coarse filter all sitting on top of the sump. The tower has a tight 
fitting lid. I debated adding the trickle chamber but after reading 
George Booth's articles on the subject, concluded that trickle filters 
were not a significant source of CO2 offgassing, although I'm guessing 
that's a debatable pointn.

    The tank upstairs has a corner overflow and because of its location 
(built into a living room wall) I don't have many options besides the 
remote filter. I could remove the tower and just use the sump but I 
would still have the waterfall effect in the piping.

    The tank is covered with a home made cover with 2 PC bulbs suspended 
2 inches above the water. The ends of the cover are open for ventilation 
so I would consider it an open top tank.

    HOB filters are not an option nor are canisters unless they are used 
at the sump.

    The SMS122 controller is new and I calibrated it to 7.2 upon setup a 
week or so ago. The reading correlates with chemical pH tests so I'm 
confident in its accuracy.

    Regarding the AAS atomizer, it's really just a misting wand for a 
drip irrigation system and while it's a handy way to have inline 
injection, I question its efficiency. Do you think I could gain anything 
with say an external Aqualogic reactor or one of the membrane types or, 
with the amount of offgassing it sounds like I have, am I doomed to have 
an inefficient CO2 system?

    On the other hand, others have pointed out that if I've got good 
plant growth and happy fish, which I have, I should be satisfied and 
quit worrying about pH levels. Am I trying to micro-manage too much?

Thanks again for your time,

    Gordon Watkins

David Grim wrote:

>Gordon wrote:
>My question has to do with the effectiveness of using CO2 injection for
>pH control. I have a 29 gallon plant tank with 2 65 watt PC bulbs and a
>remote trickle filter in the basement below. At that point I've set up
>my CO2 injection using a 20 lb bottle and an in-line atomizer from
>Automated Aquariums. Following injection (on the discharge side of the
>pump) I have in effect a 10 foot long  by 1 inch diameter reaction
>chamber before the injected water enters my tank. Even with this long
>chamber, I still get tiny bubbles at the discharge into the tank. My
>"native" water, which comes from a limestone spring, measures pH 9.3 on
>my Milwaukee SMS 122 controller. During initial setup, I was able to
>drop the the pH to my target of 7.2 over several days only with massive
>injection - to the point that a couple of "canary fish" went belly up
>and my 5 lb bottle was emptied. Now I'm injecting at a rate of 1-3
>bubbles per second and my fish seem happy but the pH has dropped to only
>8.2 where it has stabilized after a week.
>
>What I'm wondering is if I'm beating my head against the wall to use CO2
>to lower my pH or do I need an RO/DI filter for my makeup water. Is
>there a better means of injection which would be more effective, such as
>a dedicated reaction chamber or membrane injectors? Also it appears
>that, even if pH is lowered, if injection is interrupted (ie: to refill
>the bottle) pH will rapidly rise to its "native" level causing wild
>swings which would be detrimental to fish. Am I correct? Should I be
>happy with pH 8.2 and be looking at CO2 primarily as a nutrient source?
>
>Incidentally, my plants have lots of red growing tips and strings of
>pearls and are blasting- they really love the CO2 and light. Any
>insights the list can provide are greatly appreciated.
>
>  
>
>
>Hi Gordon,
>This type setup sounds like it may have been a reef tank at one time.
>
>Some of these tips may be repeats by others, but I have had a setup like
>yours (wet-dry with AAS Atomizer) with the same CO2 control issues.
>
>Provided you have no item (substrate, rocks, etc) that buffer pH, then I'd
>say you main issue is off-gassing from your filter setup. Your setup
>necessitates an overflow of some type, and with the resulting drop to the
>basement and action over the biomedia, you are probably losing a lot of CO2
>from the water that. I had the same issues with a 240 gallon tank.
>
>I also used the Automated Aquarium Systems Atomizer with my setup, and it
>really is not an atomizer, but closer to a needle valve. Nice in concept,
>but it really doesn't do anything except put out small CO2 bubbles into the
>intake of the pump return. Not much is done to break the bubbles apart
>(increase their surface area-increase absorption) or extend their reaction
>time with the water. I removed it from the 240 setup because it just did not
>work for me in this application.
>
>You should not have any problems keeping a 29 gallon planted tank using tap
>water with a KH on 9 or so at a pH of 6.5-6.8, especially at a bubble rate
>of 1-3 per second. I have a 120 gallon planted tank and keep the KH at about
>8 and have no issues with dissolved CO2 levels. I use canister injection.
>
>You should DEFINITELY calibrate the MI SMS 122 Controller. I have three of
>these, and IME they will drift upwards if not regularly calibrated, usually
>.2-.3 units of pH upward, so if your actual pH is 7.0, it will show 7.2 or
>7.3. How old is your pH electrode? These need replaced every 12-18 months
>IME. If the controller fails to hold a calibration, then you need to replace
>it. You should also have a chemical pH test kit to check the pH against the
>controller once in a while.
>
>Is your tank open or closed top? Is your wet dry open or closed (reservoir
>area-not where the bioballs are)?  Closed top systems will off-gas less than
>open top types.
>
>Personally, that type of filter setup you have for a 29 gallon tank seems a
>bit overkill to me. To me your problem is in the filter setup. You basically
>have a waterfall from the tank to the wet/dry and another when the water
>goes over the bio balls, and that is probably where you are losing most of
>the CO2.
>
>What I would try would be to remove the wet dry from the tank and either use
>a HOB (hang on back) type filter or a small canister. You will not see an
>impact on the fish regarding ammonia/nitrite if you take the wet/dry off if
>your tank is moderately to heavily planted. Your light levels are really
>high.
>
>Your options for getting CO2 into the tank sans wet/dry are to use an
>in-tank type reactor or bubbling into the HOB filter intake or the canister
>intake. The only canisters I have experience doing injection with are Eheim,
>and the 2213 (old style-WITHOUT media basket) would be what I would use.
>Media baskets in canister filters allow CO2 bubbles to bypass the filter
>media, whereas the Eheim 2213/2215/2217 Classic Series media comes in
>contact with the sides of the filter, and it the floss at the top act like a
>big plug and keep the gas in the filter for a period of time.
>
>Bubbling into a filter intake of a HOB filter is probably quite inefficient,
>but would probably work better than your wet/dry setup does right now.
>
>If you don't have an Eheim to use, then I'd try an internal reactor.
>Plantguild sells a small one with a powerhead that would work. The membrane
>type you mention (Aqua-Medic comes to mind) may work, but remember if you
>tear one membrane the other three are useless and the whole unit has to be
>replaced. Dupla makes a nice
>in-tank atomizer/diffuser that would be perfect for your application. The
>CO2 is forced thru a ceramic disk and comes out as ultra-fine micro bubbles.
>Have this under the water return from your filter (for micro bubble
>circulation) and you'd be set, I'd be willing to bet.
>
>Here is a URL for the MO place where I got mine:
>http://aquatic-store.com/en-us/dept_27.html  You can find multiple
>reactors/diffusers here. The Dupla works well in a tank your size and is not
>too expensive. It runs off line pressure from the CO2 regulator.
>
>Try the tank without the wet/dry and I believe you will see your pH problems
>disappear. I personally prefer canister injection because you never have to
>maintain or clean any CO2 reactors, but it is probably not as efficient as
>using an a specific CO2 reactor or diffuser would be.
>
>Regards,
>Dave
>
>
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>
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