nutrient deficiency

I have been carbon dosing my tank to lower my nitrate levels and would test phosphate with the API tester which I leant for all intents and purposes is useless so I bought the salifert phosphate kit and it is showing 0 phosphates. It seems like my nitrates are not going down anymore and I think...

I'm dealing with a nutrient deficiency in my tank and have resorted to daily dosing 2ppm worth of nitrate (with potassium nitrate) and dosing 0.2ppm worth of phosphate (with potassium phosphate), daily. It's 500L of water volume and I'm adding 2g of kno3 and 0.2g of kpho3. I'm adding them dry...