If you feel the CC
is the culprit, it is relatively easy to swap. You can determine if it's part of the problem by syphoning some out or taking a net and scooping some from the bottom area's. If quite black, then I would say yes. Keep in mind that even sand will accumulate detritus but to a much less degree. Sand also has much more "surface" area for bacterial colonization. My tank has only 1˝-2" of sand and still allows for proper nitification.
I recently did the same thing for the same reason back in December. After 5ish years with the CC
, I decided it was time to go. The nitrates in my sytem were no where as bad (10ppm) but after the swap, they have never gotten above 5ppm. My system is not what you would call "typical" and relies heavily on LR
and animals to keep things in line.
There are basically two schools of thought on this one. All at once or in stages.
I chose to do it in stages over about 6 weeks. Using a small 1" flexible hose, I syphoned out the CC
. I visually sectioned the tank and removed 1/3rd of the CC
at a time (every 2 wks) and added a plain oolitic sugar sand. This allows for the fauna to migrate over to the new sand as well as not impacting the biological filter base the bacteria provide. It was done with little effort and diruption to my tank (which is a full reef) and there were no loses or dreaded algae blooms.
<< is an interesting article that should also help.