if you can i would replace the cc with the sand,
there are a couple of ways it can be done, if you need the tank(or don't ahve another to put the fish in for a couple of days), but i would replace all of it
are there any downsides to adding the sand in w/ the CC? i would hate to know that i wasted all that money on the CC when i could of used sand from the start for about the same price.
Why:
Gotta ask why are you switching? Is everything ok with the tank now? If it aint' broke then why spend time and money and risk crashing the tank. However if you are set on doing it, make sure you set it up right... Read plenty of articles about it, personally I don't have one and won't be switching but like I said if you are set on it there are plenty of people in here who would love to make sure you get it up right. I am sure they will chime in
Josh
Dump the CC and use sand, its a better DSb and looks much better to boot. I set up one tank with CC and a month later set up one with sand and that was it, i changed the first to sand the week after. Just an opion Bill
the finer grains will also take up much less room for the same results, the sand has much more bacteria in a 1 inch bed than cc in a 3 inch be, and mixing it just lessens the ratio too
if you are going to add sand take out the cc..if you put the sand right on top of the cc eventuly the cc will make its way back to the top and wont look to good
I used to have a CC bed and just recently switched over. I love it. Food doesn't get trapped under the sand like it did with the CC. I am planning on getting a cucumber to help out the crabs and the starfish. The other thing is you don't have to siphon the sand. Makes it easier to keep clean.