Just when things were starting to look up...After many days of water changes (still being done daily), I finally have have 0
ammonia. Nitrites are at .25 no nitrates. I lost one platy last night, now have a danio with a bright red spot right at his gill. He is swimming fine, eating fine. Does anyone know what this could be? The platy that died showed no sign of this. He was weaker than the others to begin with, and always seemed to suffer more with water changes. The other fish in the tank are fine. It has been difficult cycling the tank with all these fish, but I have been keeping them safe to the best of my ability. I am currently cycling a 10g to move the bettas out. Any help would be appreciated.

Thanks in advance.