Uhh has anyone ever told you test for phosphates? if your phosphates are way low and your nitrates are high, try dosing phosphates. Since it's a heavy plant tank they use phosphates in roughly equal proportion so it can be one way of balancing. you may also be garvelvaccing excessively or your tank may be overstocked. My suggestion is to get some chemipure elite (1 unit) and 1 purigen packet, put both in your filter. will strip nutrients from the water.