yeah, oceanic is a clean salt mix, however, you may have to buffer the alk
(8-12dkh is a pretty good range to stay in for closed systems. the higher end of that being ideal IMO
i use different salt mixes. i try not to stay with the same salt mix 2 times in a row. i don't use instant ocean for coral tanks though. it just needs too much of this and that to get it close to NSW
reef crystals, made by the same company is a lot closer actually.
i also use oceanic, tropic marin pro reef, D&D H2-Ocean (deltec's salt), seachem reef salt, red sea coral pro, the brightwell salt, and gettanked's "saltwater correct".
i've found that reef crystals and seachem also leave that brown filth in the mixing barrel. i still use them anyway.