# What could cause pH drop?



## karen99 (Feb 20, 2006)

Is there anything that could cause pH to drop from 7.8 to about 6.8 in a day?
The tapwater here is 7.8. The tank's pH was 7.8 for a week or so with diy CO2. Then one day it was suddenly around 6.8-7.0. 
I suspect the pH drop killed three of my fish. Some of my other fish appeared extremely stressed after the pH drop and seem to be slowly adapting and recovering now. I've been doing very small waterchanges with aged tapwater which is slowly bringing the pH back up. 
But I am curious as to what the reason could be for the pH drop, so I can avoid it in the future.


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## Laith (Sep 4, 2004)

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...


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## JanS (Apr 14, 2004)

I wonder if your DIY bottle suddenly dumped in the tank to drop it that fast.

Did the room temp get higher than usual to make the yeast react faster?


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