Agreed above, looks like bryopsis. Pull the frags and dip in diluted hydrogen peroxide (70% tank water, 30% peroxide) now before it spreads through your entire tank like the plague.
I think it's time to invest in some test kits. You need to know where you're at to diagnose any potential conditions to correct. I'd recommend Ca, Alk, and Mg to test for foundation elements and NO3 and PO4 for nutrients. Luckily Red Sea has a foundation elements kit you can get that covers Ca, Alk, and Mg and you can pick up their NO3 and PO4 tests as well.