Red turf what gets rid of it.

[Canadoc]

Hey I had this problem too, that stuff just doesn't go away, and good luck manually removing it. I went and got a couple of mexican turbo snails (only have a 29 gallon tank), and they cleared it within a week. Just make sure they are actually real mexican turbo snails, and not astrea snails or any other such nonsense, I had those for ages and they didn't do anything useful

Hope that helps, they're fairly cheap so it's a pretty reasonable solution methinks. Cheers!