No plecos please - they get way too big for a 10 gallon tank. I love my mystery snails since they are small, but they poop alot so you have to be sure to keep the tank clean so ammonia doesn't build up.
Another good option for you would be 4 or 5 otocinclus. They're great little algae eaters, and only get about 1.5 inches long. They like to live in groups, which is why I recommend around 4. Three is minimum. 4 + 1 betta would be perfect.
For snails and oto's, you will need to eventually supplement when they run out of algae - algae wafers and cucumbers are great for them.
For the cause of it, too much light and overfeeding can lead to it. Try leaving your lights on for about 4 hours, then turn off for an hour or two, then back on for the rest of the day. I hear this helps with algae growth. I don't personally know, b/c I want algae in my tanks with all my snails and otos. Overfeeding can lead to overgrowth of algae because I *think* the leftovers that don't get eaten contain phosphorus which leads to growth. Could be wrong on that though.
Last edited by cajunamy; 10-11-2011 at 02:08 PM.