I started my 20g tank in the first few days of October. I didn't know anything about fishless cycling so I have fish in the tank. for the last 2-3 weeks my water readings have been ammonia 0 nitrite 0.8 or 1.6 nitrate 5-10 with API liquid test kit. I've been using API Stress Zyme and doing 40% water changes every 2-3 days. just wondering why I haven't seen any change in my nitrite levels. Any suggestions?