White fuzzy growth on coral

[SteveConn]

I've got this growth on a couple corals near the top of my tank. It does not come off without scraping ... seems to be attached to the coral. Very fine, soft fuzz.
This pic shows the worst section. Is it fungi?

Parameters:
Alk 9.5
Ca 435
PO4 2ppm
Nitrates undetectable
Temp 79-79.5
pH 8.12-8.22
Very lightly stocked 75gal + ~25g sump with skimmer, filtersocks, refugium, PO4x4 in reactor, carbon in 1 sock

I had a close call with some serious bleaching a few weeks ago when a fan fell into the water for 3 hours while I was at work. Copper leached into the system. Lost 1 shrimp and color on almost all SPS was bone white.
Added carbon and did a lot of water changes. System is stable again and almost back to full color. I had a partial dieoff off my montiporas.

Should I dip the coral? Suggestions?