Buy loaches if you want to keep loaches, not because you want rid of snails. Loaches typically only do well in groups of six or more. Only having one isn't good for the fish, and probably won't be for you either.
I got some MTS several years ago with a similar result. Got around 100, they blew up and went crazy....and then started to decline. I still have plenty, but they are not nearly as numerous as they used to be.
What is the rest of our stock in the tank? That may help people to give you a better suggestion as to how to manage it. Usually, the lack of food helps slow them down a lot. Over the long term, less than ideal water conditions can do that as well, but that might be rough on your other fish. Snails need to get calcium for their shells. "Low calcium" water over a long period of time may slow their production, but may be rough on your other stock.