djay wrote:
"Bill Stock" wrote in message
...

My tap water has always had a PH around 7.5. But lately my tanks have been
running over 8, where they used to be around 7.6 - 7.8 in the past. So I
tested the KH (5) and PH (7.0) of my tap water, which would seem to
indicate 15 ppm of CO2. I'm a little surprised to find it this high during
the summer (warmer water).

Check the phosphate level of your tap. Phosphates can bugger up a pH
reading.


I was under the impression that phosphates mess up your KH reading, not
the pH. (As the KH test isn't a test for carbonate itself, but rather a
test for buffering, and phosphates act as buffers.)

Either way, if there is phosphate in your water, the calculated CO2
value would be off.