Two Dead Rainbows !

[ShifyShify]

I got a 3 Drawf Neon Rainbows last week and they all looked ok. Came down this morning and two were dead ! They looked a bit darker color yesterday and one looked as if it was breathing really quick !

Any ideas as I really dont want to lose the last one.

My tank is 6 weeks old and when tested last week had 0 Amonia, 0 Nitrite, and Low Nitrate.

Am doing 1/3 water changes weekly.
70l Tank
Stocked with 1 Bristlenose Catfish
2 yo yo loaches
6 zebra Danios

Anyone got any ideas please

 

[alexdallimore]

are you using water treatments when you so your water change? Are your other fish behaving normal? Rainbows do change colour, my red and blue rainbows can change from really bright to dull in 30 mins at a time.