Yes you can treat it, have a look for tretment online like parisite treatment, you sure it ant fry??
They can, what tempiture are you running at. It might be good to turn it up to 26 to kill them quicker as parasites don't like hot water
those are more than likely harmless.... usually just an indicator that your tank has excess waste building up in it.
Can you describe them? how are the moving? common microorganisum that are present in just about every fish tank(whether you see then or not)- planaria, cyclops, rotifers, paramecium, and some other stuff...
ok well treatment should do if as Mikaila31 said it could be waste build up, try cleaning gravel and water then if it happens again get treatment
Luke