I had 10 yellow tail damsels in my 150 gallon tank with a 30 gallon sump, the tank is full of rocks and crevices so I was sure that they could establish their own territories, for 2 weeks they were absolutely fine, but after that I started to see 1 disappearing by the other, is this common? Besides my high nitrates (which is not affecting my snails) affect more hardier fish? I definitely did notice the nipped fins, the tank is about 1.5 years old established with growing coralline algae
