I cant comment as to why your tank is shoing no change, but i have had the
same system on a 70 UKG tank for just over a week.
I have seen a drop in PH of around .3-.5
Are you sure about the accuracy/resolution of your PH test kit?
I have two different kits here. Before CO2 both showed about the same 7.5
Now one clearly shows 7.0 the other still looks like 7.5
I think this is due to the limits in accuracy/resolution/perception of
colour with the test kit.

hth
Phil.




"NjF" wrote in message
...
Since you were so helpful answering my last question, here is another
for the experts.

Before setting up the tank I tested tap water for pH, KH, and GH (7.8,
8dKH, 17dGH).

After running for a couple of weeks with injected CO2 pH remains
stable at 7.8 with KH and GH not changing as well. The co2 system is
Nutrafin's Natural Plant System which I purchased because I had read
several posts recommending them (or at least the bubble
counter/diffuser).

As I understand it, co2 levels in the tank are directly related to pH
and KH. I don't know the algorithm, nor do I particularly care what
it is, but Chuck's planted aquarium page has a calculator that will
figure out the ppm of co2 based on the numbers you input for pH and
KH. Both his table and calculator give me a reading of about 3.8ppm
of co2 in the water, which is exactly where I started off before
adding co2.

The water is not being agitated in any real way as to cause the co2 to
escape. When leaving the end of the tube, the co2 bubbles are large,
but gradually decrease in size as they travel up the diffuser (I take
this as meaning the co2 is being dissolved). What do I need to do to
increase the levels of co2 in the water?

BTW, I get 1 bubble of co2 about every 3 seconds with about 4 bubbles
in the counter at any given time.

The tank is 10g with 15watts of light (will be upgraded shortly).

Any help is greatly appreciated. I have enjoyed reading many of your
posts already.

NjF