Sand is generally considered to be a better idea. It has tremendous surface area for bacteria to build, and is friendly to almost all aquarium life. Some folks use CC
for looks, and for some reason most lfs
push it on beginners. Unfortunately it has big places for detritus to build up, and due to it's size and shape the nifty little bugs that like to eat detritus don't fair very well in it.
You will probably end up with a healthier tank long-term if you remove the CC
entirely and replace with playsand. If you're running good exterior filtration, the impact will be minimal. If you're using a DSB
made up of the CC
, you'll have to change it out over time to allow the bacteria to populate the sand. I got started with CC
and a wet/dry and switched over after doing a lot of research. Water quality is much better now and doesn't take any work from me besides top off and sometime water changes. I like the natural approach to filtration, so i generally push the DSB
/live rock/fuge method if you're willing to do the setup.