How do I prevent/remove GSA from growing on slow growing plants?

[blink_willie]

Recently I noticed that there is some green spot algae growing on my crypt parva.It's not that much,just a few spots on the leaves.How do I remove it and prevent it from coming back again?

Thanks in advance!

[barmby]

Since nobody answers.

Do not try to tweak the system if your plant is flourishing. Solving an issue may lead to another. Sorry I can't help but say - PO4 can solve the issue. But it is risky and it is like walking around with a loaded gun if you do not know your CO2 well.