Wondering if I could ask for some opinions as to an issue I am having with a 24-gallon nano tank. It appears that colonial hydroids have moved in, and I have lost a couple of fish (a royal gramma and a yellowtail damsel). Meanwhile, a pair of mated black-and-white clowns are doing great. Question: Are the hydroids the killers, or should I be looking for another cause? The basic water parameters are good.