Ich!
The spots do appear to be spreading on the pectorals (thank you) and also I see a small spot on the fin behind the pecs. If it is ich, I have several questions maybe someone will help with.
I understand medicating can kill off the biological filter and cause the tank to cycle. True? If so, do I need to set up a hospital tank?
If I set up a hospital tank, is a 10g large enough for an 8" Oscar?
If I set up a hosp tank, how long medicating for ich before the fish is cured? In other words, how long will the fish need to be in the tank?
What is most recommended treatment for ich?
How is it likely he contracted it and how do I avoid it in the future?
A lot of questions and I appreciate your patience.