Take a small airline tube and suck it off and into a bucket, that stuff comes off easy and you don't want it spreading in your system. What ever you do don't rub it off into your tank, you'll have it every where in a matter of days. That should take care of it, thats what i did and it worked. Also you might want to clean your filters and flow tubes, it probably has come off into that as well. I use a little bleach water to clean my filters and tubes..that way I know I don't miss any, just make sure you rinse them really well. This works well with fw and sw filters. It will stop the spread of algae and wont hurt your fish if you rinse really well. But if you don't feel comfortable using bleach, atleast scrub them with a brush and use really hot water. that stuff will be in the smallest of spots and if you miss some it will just get back into your system. Hope this helps you and good luck