Hi Kanundra, the best way to deal with Nitrite is to have fresh water constantly trickling in 24/7 untill the Nitrite goes down or small daily water changes but most of all it takes time and patience, even though the Ammonia readings go down to zero the Nitrite hangs around a bit longer due to the bacteria responsible for reducing Nitrate are very slow to multiply. Ive had the same problems in the past, done water change after water change and the bloody thing still wouldnt go down it took weeks and weeks for the Bacteria to mature in the filter but the constant trickle of fresh water kept it at a safe minimum, if you do this make sure you have an overflow in the pond. | 
