A couple months ago I had some growing near my frog spawn. I did see some inside my canister filter as well. No ill effect, but as a precaution I took apart the filter to remove them. They are easy to remove and, as previously mentioned, they seem to fade away with time and will die if exposed to air (if you can do that). In a way, they are natural filters so if they aren't growing evasively then I normally just let them be. I am not particularly fond of them (same as coralline algae), but I haven't completely eradicated them because they aren't bad in my humble opinion.