Why is our fishtank being taken over by SNAILS!?

You don't mention what type of loach's the type needed are Botia's most common of which are clown loachs but these require to be kept in more than 5 and can exceed 10+ fully grown although i've only ever grown one to that size they are still large fish, other members of this family are yoyo or pakistan, blue, tiger, all of which will do the same job, Once snails get in they difficult to control without chemicals or fish of the type i've mentioned, they will increase dramatically if there's excess food so cut down on the food for the time being and check out some of the fish mentioned.