Maybe not algae, but I'm stumped

[Taweret]

So recently upon switching from API Leaf Zone/CO2 Booster to Flourish+Excel+Trace upon realizing there was prolly a good micronutrient deficit in my tank (and to hop on the bandwagon too, I guess), I noticed that soon after a grey-white powdery stuff was plastered all over the rocks, driftwood and the back of my bamboo shrimp (a fanning shrimp gathers stuff perhaps likened to moss, I guess).

It slowly goes away after a day or so and then appears again when I dose fertilizer, but doesn't fit the description of any algae I've seen in the links provided in the sticky though it doesn't quite look like a fungal thing either. It's truly powdery in appearance, like mildew, and doesn't look cottony or protrude from the stuff it's attached to, at least yet. It isn't some kind of precipitate either, as making a bit of current near it doesn't move the stuff whatsoever, but scrubbing at it does.

I'm leaning towards it being some kind of fungus, myself, but I'd like some opinions before doing anything about it.