How old is your pool liner? Sounds like a faulty liner and not ants, although I am not an ant expert (is there such a thing?). Where the liner meets the wall, is there a sharp curve with a flat bottom? If there is and your liner is old, it might be desiccating at the point of the sharpest curve, like the outside of an old tire. If the liner is new, I think the warranty should cover a replacement.

My father-in-law has an above ground pool and had problems with cheat grass puncturing his liner, so he put down the exact system FBU mentioned, and it works great. His liner has lasted longer than any previous one.