Erratic behavior/stress

Question
I changed 25% of the water and declorinated it today, now my tiger barbs, danios and sharks are hanging near the top of the tank, day and night.  Pictuc catfish remains near bottom, but breathing fast.  Chinese algae eater has taken to hiding, rather than chasing other fish.  Hardness levels had climbed recently, so seeing signs of stress I went out and bought, tested and treated reverse osmosis water, and did a further 1/3rd replacement (10 gal) change.  I haven't had the slightest signs of stress in the tank in a long time, but stress and odd behavious remins, and I am out of ideas (other than a full tank change, which I am averse to).  Filter is changed (in three separate stages) monthly, so no obvious issues there.  Hardness level down (reasonable), ammonia non-existent, ph and other tests ok, but behaviour remains.  Any other ideas?

Answer
Thanks for your question Phillip.

You have done a very thorough job and I can see why this has you stumped. The only think that comes to mind is chloromine, which according to some neutralizer manufacturers is not taken out by a chlorine only neutralizer. It can't hurt to call your water authority and ask if they have changed their recipe lately. Perhaps this nuked the filter bacteria and that is why the RO treated water didn't help. But then you ammonia is good so this can't be it can it.

With the top swimming behavior I am sure you are thinking they are not getting enough oxygen, either because the gills were damaged or there is not enough dissolved 02. Do their gills look inflamed in your opinion? Perhaps something harmed them which is hopefully no longer present. I am sure you would not have let any stray insect spray or cleaner in their vicinity. I am hoping they are improving for you as their stress must be causing you anguish also.