I woke up this morning to find my Panda Cory (Mo) dead.

I didn't know what happened but had to go to school, so didn't have time to test the tank. I came home from school about 1/2 hour ago, and tetsed the tank and the PH is down at 6.0.

It's usualy at 7.0. It is at 7.0 in my other two tanks, and out of the tap. I don't know what happened.

I test the tank regularly (about 2-3 times a week), and everything has been fine. I'm guessing Mo died because of the sudden change of PH. Any ideas how the PH could have dropped so suddenly?
Thanks
Gwenz
