Out of 21 chromis purchased a year ago, I have -2 left. Yes, -2. I have 3 of the chromis but lost 5 other prized fish to the uronema the chromis brought in and my own stupidity. Now the 3 survivors are the biggest meanest chromis I have ever seen but that gives you some idea of their mortality rate to uronema. There's a good possibility I would have more if I hadn't tried hyposalinity but who knows. They are definitely risky.From what I've heard chromis can actually be challenging to keep due to their great susceptibility to a parasite called uronema, which is hard to get out of a tank once it's in there.