I have black khuli loaches in my tank and they do not eat snails at all, they can been coexisting with the trumpet snails i have for years now.
My advise to you on what to do to cut down on your snail population, is to clean your substrate more often (particually if its gravel as it traps more matter/waste than sand) and to take the snails out yourself.
Feeding smaller but more regular meals will also help a great deal as the fish will be more likely to eat everything if they are getting 3-4 small meals a day rather than one or 2 large ones a day- this is actually more beneficial for their digestive systems as well as many small fish are evolved to have a small but more or less constant supply of food rather than two large feedings a day.
Snail populations boom when there is an excess food supply, wether it be from unhealthy plants, uneaten food, algae, dead matter or waste in general in the tank. The tank may look clean, but make sure you are keeping up on those thorough once weekly cleaning sessions and you aern't neglecting any area of the tank i.e. make sure waste isn't collecting under tank decor or the substrate isn't getting cleaned very thoroughly in the corners etc.