If you haven't used any copper based meds you should be fine to turn it into a reef tank. The selection of fish will be very limited and the upkeep will have to be top notch.
Do you want a reef tank?
Two important things is a refractometer and a liquid test kit. Something like apt.
For that tank I would get something like an aquaclear 110 for the filter and turn it into a fuge. Amazon.com: AquaClear 110 Aquarium Power Filter - for 60 to 110 Gallon: Pet Supplies
You could go with the AC70 but the 110 is gives a little more room for the macro algae.
Light I would go with a fishneedit 70watt mh 70W Metal Halide Pendant Lights
You could also go with the t5 light
Powerhead I like the koralia
Hydor Koralia Evolution Nano 425 Powerhead Fish Coral Reef Pump | eBay
Sand don't go with crushed coral because it is hard to keep clean
Live rock you can go with base rock and it will turn live I would get at least one piece of live rock to seed it and hope it has some brittle stars and bristle worms
ATO something like the nano float on this page AutoTopoff.com
Keep it down to only one fish and remember clowns do get big and can live 20 years or more and a 10 gallon is not going to give it the quality of life it deserves. Research the fish you might like and see if any of them are considered easy.
Take it slow because only bad things happen fast in saltwater tanks.