What is wrong with my damselfish?

Question

I buoght three damsle fish for my aquarium by themselves. I got to domino and one flametailed blue. The two domino fish died and the petstore people said it was nitrite but why is the blue fish still alive

Answer 1

It's a mystery unless you get testing kits for your water. If the pet store says you have high nitrite, at least you have passed the ammonium stage of the nitrogen cycle.

Don't add anything other than more live rock until your ammonium and nitrite is zero. Buy a test kit so you know.

Damsels are tough M-F'ers. Your blue will probably live the rest of the way, now that the worst is over. Be careful adding more damsels, they are aggressive. Check for compatibility.

I have two yellow-tailed blue damsels living well with a dottyback (pseudochromis diadema) and they get along fine.

This is the best site in the universe for the marine aquarist:

http://www.wetwebmedia.com/marine/index.htm

Answer 2

Some fish are hardier and healthier than others. For example, you could expose 3 people to high levels of smog or pollution or some other toxin. Two might well die, but one, the strongest one, could possibly survive.
Rather that focussing on why your one fish survived, try focussing on how to fix the nitrate problem - your blue damsel is alive now, but he won't live through a nitrate spike forever.