I get it from time to time in one tank.
Usually tends to grow on my power heads a good vinegar soak and scrub and it's gone for months. I did notice the other day I've got some on one rock right now for the first time in a long while.
IME it doesn't spread quickly and burns itself out easily. If you can get the rock(s) out you should be able to peel a lot of it off. Then water changes, GFO etc. the usual drill.
You know do as I say not as I do.
I was taught different algae favor certain nutrients and can lie dormant for years until that "special mix" is present then they'll start to grow. When their specific nutrient supply is exhausted they'll die out again. Doesn't really explain why it usually grows only on plastic in my tank but that's the general idea. :lol: