I didn't want to hi-jack another thread so I started a new one but I have questions about my fuge. lately I have been having a nutrient problem in my tank. All of my parameters are in check and I do weekly to bi-monthly water changes. I run GFO and carbon on my tank as well. My tank has been setup 3yrs. Lately I have been have problems with some corals STN'ing and I can't pinpoint the problem. I am wondering if it could be my fuge. This is how my sump is set up. On my 150 I have a 60 gal sump. Facing my sump on the left side is my skimmer compartment, in the middle is my calc reactor and return pumps and on the right side is my fuge which is fed directly from my tank. I have never cleaned my fuge and I have no critters in there other than pods. Could this be the cause of my undectable nutrients? How should I proceed. Could I vacume the sand out and replace it with new sand and start all over or what?