Odd stuff.
Is that snail eating it ?
Normal bacterias will make slime that comes off easily.
My guess is odd chrystophytes or diatom perhaps a dino. Those usually scrub off.
But with those it’s possible the nopox fueled them.
I would ignore the no3 Po4 , and I don’t prints the balance thing. As long as you have them available your fine.
Some of these organisms pull thier nitrogen right from the fish pee, and Apper to need little available Po4.
In the case of things like bryopsis, you can starve your corals to death and the bryo will live. Chrystos seem to pull Po4 directly from the rock and is a reason the root deeper.
I’d leave the nutrients alsone and figure out how to remove it. Either more of those snails , try a black out (after a couple weeks so the nopox is gone ) or scrub with peroxide.