Pictures would help. What kind of tank? What kind of light? What is your lighting schedule like? How long has the tank been setup? How long has it been cycled?
In a tank that small, I do not know what you could use to fight algae, like Flourish Excel.
A snail will help, but it is also best to find out why the algae is coming in the first place.
I'm pretty sure at this point it is because of light and heat and essentially nutrients from the fish waste that are in the tank. Algae once established usually does a fairly decent job at keeping itself there.
So at this point I am looking for somthing that will help keep it down, so I can see a bit more into my tank, and so it looks cleaner. The algae as far as I can tell isn't harming my fish, in fact it could almost be benefiting it since it will use the waste from a fish as nutrients.
But the kind of lighting that my tank gets, is a fluorescent full length desk light, so it gets considerable amount of light through out the day. Which is possibly about 8-10 hrs a day depends on when I get done with classes, and get back to my dorm.
But apple snails might be too big, and for the amount of waste I've read that they put out :/ might be too much.
I'll probably look into ordering some nerites through the pet store here, that should be fine, and have them delivered to the store so I can pick them up there.