Cleaning a fuge in a 12 NC DX?

[FreakShow]

I am currently running the first and second chamber of a 12 NC DX with rubble and Chaeto. When I change water once a week, I pull out the Chaeto and rinse it with the tank water, trim it if it’s getting too big. I vacuum out the debris from the main tank area, I'm BB, so this is easy. I try to get up under the aquascaping where I can.

 

After the cleaning the tank looks spectacular, crystal clean. Then I start to add the new water. I usually add it by slowly pouring it into one of the back chambers.

 

When I turn the pumps back on they spit out untold clouds of sh*t. The water is cloudy but it all quickly settles on the bottom and across all of the coral! It looks like it just snowed in there, like I hadn't cleaned the tank in months!

 

I figure its coming out of the rock rubble. I started to stick the siphon down into those chambers and pulled out a lot of detritus but it doesn't seem to help.

 

Any thoughts?