I have a five year old gf with what appears to be a patch of green algae just to the left and rear of the dorsal fin. The fish does not appear stressed and the water quality is good except for the salt level which was a little low after "opening" the pond from winter. Any ideas?

Algae does not normally grow on healthy skin/scales but it sometimes grows over a wound or over fungus. Perhaps a water change and some more salt might help?

I think I would try to catch the fish and swab a little hydrogen peroxide on the patch. Make sure not to get it in the gills! This will take care of any possible infections. I have had algae grow on snails, but never heard of it on fish. Can you post pics? Good luck!

Sounds like a fungus and I believe proform C will take care of it.

Scott