Other then the fact sailfin mollie sare true brackish water fish, and most mollies should have some level of salt in their water, or they become very prone to bacterial infections. I doubt it would be ick. most cases of "flashing" i've seen appropriated with a disease ect is due to "velvet" which is often mistaken for ick. as they fish develop dots, and the typical velveting over their scales. If an of your mollies are new thats where i'de lean my guess towards. You gave the perameters for everything but your Nitrites. If you don't check those.. I'de check those as well, I've seen spikes of this in otherwise "perfect" water conditions. That can also cause flashing. I doubt this is the case with your set-up, but rule out what it isn't to be safe. I'm not sure about the exacts of the doseing but I'de consult with soem of the other live plant tank owners. BUt may be wise to cut-back stop doseing for a few days, possible build-up of some trace that may potentially cause it as well. and unless you have very delicate plants shouldn't make them any worse for wear. and of course replace the UV bulb asap.