If your fathead base is fine, I would leave it alone. My fathead base in a 2 yr. old pond is gone. I introduced Gambusia into my pond to help limit reproduction of all species, I believe it works...a little \:\) In the Spring, they are everywhere robbing nests & young. Around mid Summer their numbers peak. They are really not much for a larger fish to eat, but they seem to serve a small purpose. Some studies show they really don't have much of an effect at all in a pond.