Tank upgrade

[Marcus K]

My 90gal seems to have some colour change on the bottom seal of the tank. For some reason it has changed to a brown colour from black so I figure its time to change or reseal the tank. I am looking into another tank that is larger but need some advice on how to change over. My current tank has flatworms, the brown type that look like a spade. I have dosed with a home brew flatworm exit that killed most of them. But they are starting to show up again on my mushrooms. I like the look of CC over sand and do not like the BB look so should I move over my CC or start from fresh? I plan on getting the new tank set up off to the side of the old tank and get it up and running. I was thinking of dosing the tank for the flatworms again and then move over the corals and LR.
Am I missing anything?