I have a 280gallon 72x30x30in tank stocked with 2 silver arowanas, 3 cichla monoclus, sturgeon, 7 silver dollars, indonesian Tiger and an oscar. Nitrates are at 80ppm and it would never come down despite a huge water change. I use direct tap water + water conditioner as my water source. Can you recommend some ways to lower my nitrates? Thanks!