White bug things eating coraline algae

Regarding the pic, it's my camera that makes it look so odd. It doesn't look green at all 'in real life'. Every second pic I take seems to be green. The lighting is a 4 ft one of these Detailed Product View

I don't mind having the things if they're not going to do any harm, but they do seem to eat coraline algae, assuming that's what that maroon coloured stuff in the photo was on my tank (that patch is all gone now).

Thanks for the info anyway, I'll look into other reasons why the tuskfish is getting depressed.