I tested my water using API test kit, and it read 20+ ppm for Nitrate. Even I did not dose Seachem Nitrogen, the reading is constant high for Nitrate. I think it is from fish poo and fish food. It is a planted tank with fast grow stem planted, like rotala, HM, glosso, downoi.
Do I still need to dose Nitrogen? If not, do I need to dose Flourish Phosphorus? Fish food contains Phosphate too. I tried to use API test kit to test Phosphate, but it seems not very accurate.