Chill out before you freak out.
What water are you using? RO
water or tap water? More than not, the tap water has trace elements in the water column that will cause some serious and some nasty algae growth. As well as diatoms. I would also consider getting more snails, as a "couple" just won't do. Don't go overboard and get like 50.. but a reasonable number of snails should be added to your tank. I have a 55G and i have 8 astrea snails, and they pretty much destroy all of the algae in my tank. It's quite amazing what such a small number of them can do. Anyways, what are you feeding the fish, how many times a day? If it's frozen food, do you rinse the food before you geed it to them? Frozen foods usually have phosphates on the outer coating, for reasons i have no clue, but they just do. Phosphates also cause algae problems etc..
What are your lighting cycles? How long do you keep them on during a day?