How often do you completely drain and refill the water?

I notice that I can see right through your netpots where the hydroton doesnt fill all the way up. Take a paper or styro or plastic white plate, and cut a slit in it form the edge to the center, and cut a hole for the stem in the center, then slip it on upside down to cover the netpot so no light is getting into the water.

It's possible you could have algae trying to grow or something and messing up your PH also.

You should notice tomorrow when you drain it if anything nasty was going on in there.