I had 3 azure damsels in quarantine for 3 weeks doing well. My lfs got 4 more in so I snagged them and added them to the quarantine tank. I put a divider in the quarantine just I case. The four recently added have slowed died over the course of a week and a half. I’m not sure what’s causing their death but would like to prevent whatever they had from spreading to the otherwise 3 healthy ones. There are no visible spots or sloughing. They seem fine then the next day they are at the surface gasping and have a slightly sunken belly with a black spot at the base. I have tried fresh water dips but haven’t noticed any parasites or worms coming out. Thoughts?