Hello everyone! I started my tropical fresh water (20 gallon) aquarium in February. I've had bad luck; the ammonia level is always high and hasn't stabilized yet. I change the water weekly (50%) and use stress zyme and an ammonia reducer. Shouldn't it stabilize yet? Do I need to get a second filter to help? I have 3 fish now; 2 tetras and a pleco. The ammonia level is always at 2.0 TIA!