You'll need to start from scratch really, clean it all up properly making sure nothing remains there, buy the salt, substrate and some decorations if you'r going for fish only. If you want a reef it's alot harder, you'll need a skimmer, live rock always helps and makes it look nice and has alot of beneficial things on it and then you must buy food for the corals (plus feed by hand depending on what corals) and of course a MUST upgrade the lighting to metal highlights is usually best.
I say start by a fish only see how that goes and then little by little see if you want to ventrure to reef keeping which is a whole different world added to marine keeping.
It's all good stuff it just needs getting used to and is not hard to maintain once you know what to do etc.
If you have ever used copper in that tank, consider getting a new tank. Check out a few of the larger reef forums, such as www.reefcentral.com for tons of info. And as always, ask away here, we are happy to help