My fault - trying to get caught up after being away. When he left the water out - did he aggitate the surface? He might try the experiment again, but put a little bubbler in there and see what happens.

What kind of substrate do you have, zambize? Any rock work or decor?

That could make a huge difference so he should try it out if he has not.

A natural way to lower the pH is to put some peat in the filter or as the substrate, but I don't like messing around with pH too much so I'm not sure if I recommend this or not. I know I keep some petrified coral in my tank, but I don't go crazy checking the pH and adjusting it.

If I were you, Zambize, I would buy a little airpump, some airline tubing, and a little bubble stone. Put the stone in a bowl of water, let the water sit for 24 hours with the bubble stone aggitating the surface, and then check you pH. If you get a high pH, then just go buy a 5 gallon bucket, put the bubbler in there and let it sit 24 hours before your water change.

P.S. I have never kept your specific fish before. have you looked up how sensitive they are to pH fluctuations? We may be going a little bit over kill here.