I recently bought 3 blue/green chromis from my LFS. I have bought all of my fish from this one location and have had great success. When I added the fish to my tank, I noticed that 2 of the chromis had a white spot on their back tailfin. (I used the drip method of acclimation which took approx. 2 hours) I wasn't concerned because I saw no spots anywhere else. I checked the tank 2 hours later and noticed that the 2 chromis with the spot on their tail were dead, but the chromis without the spot was still living. I immediately removed these fish and rechecked my water:0 ammonia, 0 nitrite, 20ppm nitrate, 1.024 specific gravity. I did a 30% pwc as a preventive measure. Today the living chromis appears to be thriving in my tank. Is there anything else I should do??