SRAC reports say that tilapia can handle nitrates up to 300 ppm, but only about .5 ppm ammonia long term. The problem with ammonia is that it spikes, and seldom rises slowly.

In AP you seldom if ever need to do water changes. The key is to never remove or add too much fish or plants at anyone time. Just like water changes, the 50% limit applies, and you are better off with 25% harvests.