"Dave Millman" wrote in message
...
Paul wrote:

Checking the CO2 in mid afternoon I find that pH is 7.6 and KH is 10dkh
=
7.5 ppm CO2, in the morning after lights on for a couple hours it
checks, pH
7.0, KH 9dkh, CO2 = 27 ppm. Is this depletion good, bad or indifferent.
Should I be looking at decreasing my surface agitation of the power
filter?
Thanks.

Paul,

It is unlikely that KH would swing 1 point in a few hours. I am guessing
that
you are measuring pH and KH, then calculating CO2 from them. If so,
inaccuracies in the KH measurement are causing wide apparent CO2 swings.

Is your test kit fairly new? Mine allows doubling the accuracy by doubling
the
amount of water. Does yours?

I have the Aquarium Phar. test kit, about 10 months old. When I checked the
KH at 9 drops(9dkh) the water just started changing color to yellow, it
took one more drop to completly change it to bright yellow. I double checked
it with a newer Tetra Test kit which agreed with the 10dkh of American Phar.
The second test was definitely 9dkh. So maybey there was 1/2 point diff. The
Tetra Test does allow more accurate testing, will have to give that a try.