Corydoras dying slowly
So for the past 2 to 3 weeks now my 5 corydoras have been dying slowly
one by one. 1 has already died. 2 and 3 are now breathing heavy and not eating or moving around...slightly tilted on the ground.
There are no visible signs of sickness such as white spots/flakes, bumps, redness or injury. They look fine from the outside. But one thing I noticed about the heavy breathing is when looking from the top view down, the gills
of the cory is really open and expanded. Usually the gills are nicely tucked in by the sides even when breathing....but now they are really wide open and sticking outwards.
I've done water changes several times (30 to 50%) but no improvements.
I can't figure out what might be causing them to be dying so slowly.
Should I just take them out of the tank and put them in a separate container for a while to see if the completely new water might be good for them.
I didn't do a 100% water change as I heard that's not good, but if there's something in the water that is killing them (maybe plastic plants? tape?) then moving them to a completely new environment might be good?