A couple of years ago I had an ant problem too. Subsequently had a liner leak. I had already covered the pool for the winter by that time, so had a leak detection guy out to put on a dry suit and sleuth out the leak in the cold water under the cover to patch. He said that the leak was caused by ants behind the liner.

I usually get ants every year, just not this year. Since I have several pets, I put out the common ant bait traps bought in a hardware store, and in about 48 hours the ants are gone.