I have a rainbow tank at home and just found out the other day one of the heater had failed off.

This caused the tank to drop to about 22deg C for about a week..... Fish where a bit slow and didn't eat much so I started checking and realized the heater was faulty. Replaced the heater last night and brought the tank back up to normal temps... about 25 deg C.


Today I noticed a couple rainbows with a red tummy. One is fairly bad (pic below). Another is similar and a third has a red dot starting to show on it's tummy.

Testing the water, everything seems fine.....
ammonia, nitrate, nitril all in spec. PH steady at 6.2-6.5 (tank is co2 injected).

What could have been the problem, and more importantly, what can I do.

I do have some cory's in there and a loach so adding salt is a bad idea (at least in large amounts.

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