Thanks for the reply!

OK, I checked the 7.01 pH buffer solution with a colorimeter - the only
pH gadget I can rely upon. It gives 7.0 pH. I noticed that the pH probe,
which initially read 6.85 pH in the tank, drifted over 30 minutes to a
stable 7.05 pH. The colorimeter also concurs with a reading of 7.1 pH.
Everything is now in agreement. But a pH of 7.05 translates to 37 ppm of
CO2 with my water. Woops!

I reckon the buffer solutions pulled the probe's readings down
temporarily. Is this known to happen??


Nikki


I wouldn't be concerned with a 37 ppm of CO2. I keep mine around 30 all the
time. Great for the plants.

Rick