Snails are good for the tank. They're the best cleaning crew. But, if you have too many, they can add to the dissolved waste material in the water and affect the water chemistry. If you think you have too many, you're likely feeding too much. Snails are a great way of determining how much to feed. I suggest slowly reducing the amount you feed and you can drop a couple of lettuce leaves into the tank. Snails can't resist lettuce. When the snails gather on the lettuce, remove it and throw it away. You can also crush the snails with a wooden spoon, the fish will clean up the mess in no time and the shells will dissolve in the tank water.
"Fear not, my young apprentice. Just change the tank water."