High Nitrates

[Rob Rudow]

I have a 650 gallon tank with an additional 600 outside in the filtering system . I have had this tank for 16 years. I have success with fish and soft corals but cannot get hard corals of any kind to grow long term. I have a complete dosing systems, refugium, two skimmers , and I float extra carbon bags. I cannot get the nitrates and phosphates down enough to sustain SPF and other corals. I do 100 gallon water changes every three weeks. The fish completely eat all food within 90 seconds. Any suggestions

 

[blaxsun]

What are "high" nitrates? Because I have SPS corals that do really well in my high nutrient system.