to help the experts (which is not me!) they will need to know if you added water conditioner/dechlorinator.. and the water parameters like pH, Ammonia, nitrite, nitrate .
If you don't have those tests kits , its worth gettign when you can.. i had no idea my nitrates could creep up despite good regular water changes before I got my nitrate test.
What about aeration,, is the water well filtered/aerated? If they're all hanging at the top sounds liek they need oxygen.. are there gills a normal colour? ammonia can cause more red/pink than normal gills.