its counterintuitive to want an algae eater who eats snails. Generally, obligate herbivores that eat algae woudl not seek out a protein source like snailsnor have the proper mouth/teeth to be efficient.
As mentioned,assassin snails do a good job eating pest snails, but will reproduce as well.
Best bet is to bait/trap the pest snails, figure out the source of your excessive algae and curtail it.