Micro sized parasites?!

I've got a 5.5g tank with one betta and 5 snails. It's been like this for about a year.

Today, I discovered that my tank is infested with these teeny tiny dots that are swimming around. They seem to be affecting one of my snails as he will not come of of his shell at all and these parasites are crawling all over him.

What are these things? How do I get rid of them? I'm going to the pet store today so if you could give me some tips I'll pick something up while I'm there.

THANKS!!!

Nitrate - 40
Nitrite - 0
Hardness - 100
Alkalinity - 40
pH - 7.2

The picture you see is a piece of cuttlebone I took out of the tank next to a quarter for size comparison. The tiny brown dots are alive and moving all around the tank. I could not get a decent picture of them swimming in the tank because they are far too small. I have taken my betta and snail out of the tank and put them in clean water temporarily until I find out what to do. Please help me!