In article .com, hearse71
@hotmail.com says...
I am using a small garden fountain pump in the sump to pump clean
water to the reactor where the co2 and bio balls break up and help
disolve the co2. from the reactor back to the sump where the co2
enriched water should be pumped back into the tank. Problem is the ph
in the tank has not changed since day one. the co2 test kit registers
nothing. so i take the return hose coming from the reactor and place it
directly on the intake of the sump pump. it took 3 bubbles per second,
the little fountain pump on its highest setting and my tank filled with
thousands of tiny bubbles for the ph to finally lower from its regular
7.6 to its now 7.2.

It's hard to say how effective your system is at dissolving the CO2 in the water.
If bubbles are coming out, then it is not completely dissolving the gas that goes
into it. Perhaps the bubbles are floating up a side wall and not really mixing as
you expect. I think that some commercial designs make the bubbles float up into a
downward water current in order to maximize contact time.

I find the little Hagen bubble ladder to be easy to use, although a 75g tank would
be at the limit of what it could carbonate. I base that on experience with a 37G
tank with light-moderate surface turbulence, in which a high bubble rate can drive
the CO2 higher than I prefer. A convenient feature of this unit is that you can
see the bubbles entering the ladder at the bottom so you have your built-in bubble
counter. Then you can see the bubbles getting smaller as they rise up the ladder.
You can be certain that you have a certain number of bubbles dissolving into the
water column. You might wish to try one for comparison. They are about $10.

Two other things come to mind. First, the CO2 will take a while to come into
equilibrium. If you make a change it will take hours to see the result. For a
small adjustment, it might take a day before you can tell the final value. Second,
the CO2 is always leaving the aquarium at the surface. If you have a lot of
surface rippling and not much of a cover, then you could be losing a lot of the
CO2 that you put in.