I don't know if there are any horror stories posted from useing bio pellets and I have'nt read all this thread about them. I want to share my story in the hope that this will not happen to your tank! and possibly learn why this happened to mine! I have a 180g with 35g frag tank and 100g rubbermaid sump it has been running for 2 years, I had many sps colonies that were doing well. I picked up a calcuim reactor filled with media about 4 months ago and shortly after that I developed red slime, My phosphates would test .5 and my no3 was 15ppm, I continously ran gfo. I do a 30-40g water change every 2 weeks. I could not get rid of this slime, my lfs recomended dosing mb7 so I did that for 3 wks, 8 caps a day, still had it! So I read about the pellets and that you need a huge skimmer and I have a SWC 300 skimmer and to use less than recomended pellets (800ml) for the capacity of my system so I started with 300ml in a phosban 550 reactor with a mag 5 pump. They ran for 3 wks with no change so i added another 200ml for a total of 500ml after a total of 27 days I came home monday 6/27 to a cloudy tank and all the sps faded and clams, p's & z's, lps all closed. I immediately disconnected the reactor and did a water change, My lfs recomended I feed the fish more because the pellets brought the nutrients down too low, so I did that for a few days as things continued on a downhill spiral! I did'nt even think about having an ammonia problem until 4 days had passed and things were still getting worse! I have over 200# of live rock and 75# of sand in the system. I tested it on thurs .25, I have done 4 40gwc and today i'm at .1. for the last few days I have been clearing out all the dead! Talk about stink! my wife is freaking out about the smell and the tank and sump is in our basement! I'm adding mb7 in the hopes of rebuilding my bio filter. The fish look and act normal no problem with them yet and some things are beginning to open up and look a little better after all the water changes. I have finally rid my tank of the red slime! and all my sps colonies and 2 clams so far!