i would definitely not do a blackout on that tank, personally.
i'm going to stand by my original post and add...
manually remove as much of that as you can whenever you can followed immediately by a large water change each time.
cut down on your light (i know i'm repeating my self here, but... ) if you have to, only light the tank every other day.
remove that nana from the tank, clean it up good and re-place it back into the tank under your lotus to give it some shade.
i'm going to stand by my original post and add...
manually remove as much of that as you can whenever you can followed immediately by a large water change each time.
cut down on your light (i know i'm repeating my self here, but... ) if you have to, only light the tank every other day.
remove that nana from the tank, clean it up good and re-place it back into the tank under your lotus to give it some shade.