In regard to your rising nitrite level, I can think of a couple things you could do to help these nitrite levels lessen.
1. Feed your fish only what they will eat right away. No leftover food degrading into your tank ecosystem to give you an ammonia spike and start the cycle to nitrite.
2. Add some live plants: chaeto is great and will suck nitrite right out of the water. Plants are great for stopping the nitrate cycle and making your tank safe for your fish.
Hope this helped