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[APD] CO2 and pH control

This is my first posting to a list I've used many times over the years. 
I've searched the archives unsuccessfully for an answer.

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.

Gordon Watkins
Parthenon, AR
Aquatic-Plants mailing list
Aquatic-Plants at actwin_com