Hello Dee...
If there's a lot of snails in an aquarium, that means there's too much dissolved food in there too. You're feeding too much. Aquarium fish have a stomach the size of one of their eyes, so they don't need much to eat.
Plants are the same, very small and don't require much. In their natural living places, they're lucky to eat once a week.
I feed twice a week, just a little and what will be eaten in a minute or two tops. Gradually reduce the amount you feed and the snail population will drop accordingly. There won't be enough food to sustain all of them.
An added "perk", no algae problems either.
B