Sloppy I flushed the rockwool I had in my net basket. I took a cup of water from the rez that was ph'd and just slowly poured it on top of the RW cube to try and rid of any stale water or build up in it that may have caused my problem. Then when I did my rez change, I did it again with just plain ph water to flush any remaining nutes out of it. Then made sure the water level was well below the basket to prevent the cube just sitting in water.
I've read a couple stories of people having problems with their dwc and turned out to be their RW cube.
Does your DWC have a drain, or do you take the lid off and pour it out??