They won't. The odds are they were raised on floating catfish food. My Tilapia are happy to eat the fish food, but they are still doing a wonderful job keeping the filamentous down to the lowest level ever for this time of year.

I am not sure what chemical control you are using. I do wonder if it might harm Tilapia which are consuming the algae. I'll bet others here have had experience with such a combined apporach, though.
Lou