As Cannonman and Bigarn said, it will go away.
A good clean-up crew, and good water circulation will also help (Besided just being a generally good idea anyway).
A "Clean-up crew" usually consists of snails, maybe some hermits, and possibly certain starfish or other things like sea hares, sea cucumbers, urchins. They spend their time looking for and consuming things like algea and other growths, leftover food, as well as detris (poo-poo).