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Re: [APD] CO2 and pH control

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

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.


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