It's a water mold. You could try scrubbing everything with tank water and a new toothbrush, and then letting it dry completely for a few days, which will kill the mold on them. But with stagnant, dirty water in the tank, it'll probably come back. If you leave your tank lights on too long, that won't be helping either.
How much/often do you feed your fish? Even if you're not overfeeding, fortnightly water changes in a small tank in which a fish is fed and defecating will result in a huge level of waste that is feeding the mold. I strongly suggest that you also increase your water changes - even once a week is nowhere near enough to prevent harmful ammonia building up in a tank that size, this encourages mold and it's really not great for your fish either. For an uncycled tank that size, 1 x 50% and 1 x 100% water change per week is best to keep ammonia levels at a minimum.
Also, increase air circulation in your tank - having an adjustable-flow or baffled or even airstone with the pump on lowest setting will not cause too much flow for your fish but will help prevent it.
Last edited by Aus; 06-18-2012 at 09:00 AM.