Since I have no idea of what species it is, I can't say rather it's good or bad. It does resemble the one listed as a herbivore in the one link I provided and I'm leaning in that direction but I can't give you a positive. You would need to watch and see. As for getting rid of them, if they aren't parasitic, I'd leave them. They just add more diversity to the tank. If you conclude they are parasitic (notice them attached to your fish) then you would need to remove the fish and leave the tank fallow for 3-4 months to starve them out. There is more detailed info on this in the links I've posted.