DEFINITELY don't give them any nutes...FFOF should be plenty for them. If those are t5's I'd pull them back. despite the chatter about flouros being so close I find t5's run hotter than other flouros and benefit with the lights a bit more away.

The rust spots may/can be sign of a k def if not pests......BUT.......you need to understand that that is just a symptom.....not a true issue. Things like overfert, high ph, low humidity (like your T5's being real close) tend to present first as a k def. FFOF is not lacking in ANY nutes.

So the problem must be ph lockout or lighting too close or bugs. Since your water is good ph you say; pull your lights back .

WW can be delicate......ease up on the lights even if just to help ease stress on the plant. That may or may not be your only issue; but it's a fine place to start.