I have a fish only 100 gal tank with 90 lbs of live sand wet/dry w bio balls, fluval 405 and protein skimmer run by a rio 600 venturi power head. It all works fine. I had it set up for 15 years without the sludge build up caused by the protein skimmer. The tank was broken down for years. It's been set up for about 11 mos now and it has the issue of very quickly building up a dusty brown sludge in about a day. The nitrate level never gets above 40. I have tried all the traditional fixes. Large water changes. several consecutive small water changes sucking out all the feces on top of the sand. cleaning the fluval every two weeks instead of once a month. I put filter pad at the return side of the skimmer which goes directly back into the tank which helped a little. I changed to a 50 micron polishing pad that I have to clean daily because it is filthy. The problem still exists. The build up on the rocks and sand is just slightly slower. when the tank set up before I didn't have this problem. all the equipment is the same. The only difference is the live sand. Caribsea original, oolite, ocean direct, fiji pink. I have now tried turning off the skimmer and the problem has really slowed down. Could the problem be using Zoe marine to help heal injuries on my Niger?