It may be saprolegnia or columnaris, which is caused when your fish is in poor health and water quality is also poor.
I would step up the water changes and make sure you are gravel vacuuming thoroughly.
In an uncycled tank you will need to do 100% waterchanges to get rid of all the ammonia, if not you are just diluting it when you do waterchanges.
I had this recently in a tank that I though was clean and had low ammonia ppm so.. I tore it down, QTed all my fish in AQ salt
you can read about it here: http://www.bettafish.com/showthread.php?t=69564
I also gather snails poop a lot so it could be adding to the need to clean, vac and water change more often