how old is your tank? its pretty normal on young tanks, but the best way to get rid of it, IMO, is to do a water change 10-20% every other day for the next week, it'll be gone by the 3rd change. now how to keep it gone, mind how much you feed, every time i had an outbreak it was due to overfeeding. every piece of food in your tank that is uneaten, is food for that slime.