03-16-2006, 11:34 PM
Join Date: Sep 2004
Location: Geneva, Switzerland
One possibility is CO2 injection into a tank with extremely low KH (less than 2 or 3). Since the KH buffer is so small, the pH can suddenly drop significantly.
Check your KH, even if it's normally higher than 2 or 3. Sometimes the water company suddenly uses another source of water with completely different parameters. Here sometimes the water utility will not have enough liquid rock water from streams and wells so they suddenly start using lake water: KH goes from 15 to 4-5 (I wish they'd stick with lake water!!). I learned of this the hard way when I was using a pH controller and not regularly checking KH.
I can't really think of anything else that it can be, other than a bad test kit/pH probe...