Keep up with maintenance, maybe be a little more frequent, feed a little less (watch and see that all is consumed) and the numbers should stay in check. I don't see any reason to panic. I can't keep them alive. I see a few here and there, barely measurable. I keep ramshorns in the 180G planted along with the nerites, and the ramshorn numbers ride the tide of my maintenance schedule. If I slack off just a bit I'll see a few here and their. A few days after a water change, they seem to all but disappear. The Nerites in that tank don't even notice the other snails; the occasional pond snail or MTS. Nerites are MUCH more fond of film algaes than anything else.
"Why can't my wife see all of this stuff as an investment?"