its detritus built-up. all that crap from the sandbed are released when it was disturbed. just blow the hell out of it and catch it up with a filter sock.
Well today I couldn't take it anymore. I removed all rocks and put in another tank to keep wet. I removed any remnants of sand left in the tank but it looks like a sand storm in there right now. I added a 100 micron sheet in a wet/dry tray and keep rinsing it out when it gets completely dirty. Did a 40% water change. Problem is sand is clinging onto EVERYTHING! So I aimed powerheads in every direction and cranked up the closed loop. It'll probably be days before sandstorm ends and I can put rock back in.
Hi,
Not possible to take any pics anymore. Rocks were cleaned off and put in another tank. Today my Mag 24 arrived and I hooked it up to my closed loop system. I'm filtering the heck out of the tank and trying to remove all remnants of my sandbed I removed. I now realized that even though the sandbed was gone you guys were right. There must of been dirt & waste, microscopic particles in the water from the sandbed that clung to the rocks and built up. It looked like the dust you find in a vacuum cleaner bag. Since I am just converting the fowler to a reef I can take my time to filter the water with 100 and 200 micron pads. I've been washing them out every hour or so as even though the water looks pretty clear they are picking up loads of the sandbed thats still suspended in the water column. My live rock is fine in th other tank so I don't plan on putting it back until the micron pads pick up no more dirt. There is still plenty of rock in the refugium and sump.