This tank was started in October. All the rock was used from a previous tank and set up. There is a large shelf of Tonga rock I think may be trapping detritus and other things. I did not see a lot of CUC in the tank and it is a fairly well stocked 300g DD. I am more or less the designated troubleshooter. Both Po4 and NO3 are high and I think it has largely to do with a lack of flow and how the tank is set up.