I know this isn't Tilapia control but when I first started looking at my pond it was super over populated with tiny BG and what looked like a million shiners. It's a 1 acre pond. I added 100 F1 bass and it took 3-4 years to get the pond close to balanced. It was 5 years before I started pulling any bass out. Last year was a major bass cull. I say that to say it may just take longer than you would like. I thought after 2 years all my bass had died, then the next year they were blasting the top of the water like mad.