If I check my fish tank's nitrite and nitrate levels do I still have to check the ammonia level?. Thanks.?

Ammonia build-up is responsible for most fish deaths in aquariums. Testing for ammonia should be your top priority. Nitrite and pH should be monitored frequently, too. Nitrate should be monitored at least once a month and the levels should be 20ppm or less. If your fish become lethargic and overeating is not the cause and ammonia and nitrite are both 0ppm, test nitrAte. High nitrates can cause lethargy in fish.