One of my Dalmatian mollies seems to have a large white hole in its side. It’s the only fish in the tank with this symptom. The tank has 10 mollies, 10 corydoras, and 5 bristle nose pleco. It is a 70 gallons tank. This fish is a baby that was born and raised in my tank so likely not a disease from a pet store. No recent additions to the tank. Wondering what it could possibly be.
ammonia - 0
pH- between 7-7.5
Nitrite - 0 ppm
nitrate - about 20 ppm
KH - between 40-80 ppm
and GH - 180 ppm
water temperate is 79°f
I do a 25-50% water change every 1-2 weeks