"teenage" Molly Fry Has White Pimple Above Pectoral Fin

[wendyngd]

He seems ok otherwise-and white pimple looks like it opened and is just a shell...I have been treating the tank for an ammonia spike and white thread algae. Mysteriously lost 2 adult mollies separately in last few weeks. This time, I think I might have changed too much water last time...\


Anyone ever experience this or any suggestions? Thanks. -Wendy