sorry this is long (it seems I got out of hand)
sounds to me you have too many nutriants in the tank, sparking an algae bloom, snails love algae, among other things
the snail population may (oddly as it sounds) be balancing the algae bloom and keeping the algae down. removing the snails will unfortunately let the algae get out of hand, unless of course you can find a fish that does an absolute fantastic job on algae
Oto's can do a decent job, if they feal like it, (mine dont)
unfortunately I cant think of any fish that do both algae and snails to the degree your looking
Heres my experience
my 20 gallon community
no algae(or negligable)
probably had about 500 snails in there (waaaay out of control)
did the great snail massacure killing just about all of them, thourgh vigourous sand removal and dumpoing and boiling and replacing(it was a dark day for the snails)
well shortly there after I started a planted tank, got the CO2 going micro nutrients and what not (lots of info in that part of the forum) and wouldnt you know it the plants started growing like mad
ran out of micro nutrients and yeast (need to go shopping) within about 12 hours my tank was green with hair algae
today I found snail eggs(which i squashed of course)
so your looking at either getting a snail eater (botia loaches are good if you can fit them in)
a good algae eater (otos can be good)
or perhapse cutting back on feading and doing more frequent water changes to remove excess nutrients, leaving the light off for a longer period of time (perhapse putting it on a timer) add plants to take in excess nutrients
thats all I can think of though
good luck