A big spot on my puffer (and it's not a spotted puffer!)

[hillegom]

Originally Posted by jassz

I don't get it... if the algae takes nitrate and phosphate out of the water, shouldn't I leave it? That's a good thing, isn't it?

Yes it is a good thing. But if the algae dies, it will just release all the nutrients it absorbed . Best to take it out and let new algae grow.
A lot of people put chaeto in their sump, and harvest that, for the same reason.

The anemone looks suspiciously like a majano pest anemone. But not 100% sure