My nano tank has been set up since new year and houses a green chromis, yellow-tail damsel, domino damsel and lemon damsel fish. They were introduced at the same time as each other.
They have been tankmates for about 3 weeks now and the water levels have been good pH 8.3, nitrates <0.3, ammonia 0. the temp maintains around 27C. However there have been two occasions where I have found my normally dark blue lemon tail, pale silver (almost white), the chromis looked really scared hiding and gasping and the lemon damsel showed black stripes. The domino looked completely fine.
I checked the levels and they were fine, but carried out a 10% partial water change. This seemed to work very quickly and they returned to their normal colours. Then a week later. it has happened again. I carried out the change again and they returned to their normal colour and the chromis came out of its hiding place for a while.
The next day they looked horrendously pale. Yet when I came home from work they looked fine. But the domino was chasing the others around the tank. A friend suggested bullying. So I have removed the domino.
Any thoughts or suggestions???