Interesting that 1077's scheme is near identical to mine, in terms of T8, duration, ferts.
My floating Pennywort does get algae, but it grows so fast that every week I could (if wanted) trim it back to discard all the algae-covered growth. I do this periodically, depending how much floating plant cover I want in the tank. I'm happy seeing algae on the floating plants rather than having to fight brush algae on the lower.
You (Inga) didn't mention the lower plants and the present duration. But as this tank had some real issues recently, the "balance" is obviously upset and algae is very quick to take advantage of such situations. Just as algae is more prevalent in new tanks for the same reason. Once things are balanced this will likely not be problematic.
I would not resort to Excel. It is not needed to begin with, plus it does detrimentally affect some plants, and it will raise the "balance" higher which may well cause more algae. It is safer to reduce duration to achieve a better balance naturally.