White spot on clown

[nurjrk]

I've noticed this white spot at the base of my clown's left side fin where it meets the body. It looks more like a (excuse the term) zit, as it does like cotton or cauliflower. If anything it may be a bit fuzzy. Just did a 20% water change today, tank and sump = about 65 gal. Amonia, Nitrite, Nitrate are zero, Ca is low at 250 (just started with Ocean's Blend two part) and Alk about 3 meq. Those are the only tests I have. He is the only fish in the tank which has been up for 3 1/2 months, fish has been in for about 2 1/2 months. 50 snails are the only other things in the tank. He has been eating well, and very active, does not look or act "sick" at all. Picture is the best I could get. I don't have a QT tank, but could get one tomorrow if need be.
Any help would be greatly appreciated.
Thanks,
Jeff