The rocks are dead, they don't die. Photosynthetic life on the live rock may die from lack of light, but adding light before you are done cycling/curing will just create an algae farm.
Do you have test kits? If so what is the ammonia, nitrite, and nitrate? You should be pretty well along in cycling (which in a tank with live rock will coincide with curing the rock). You should also have your own test kits so you can monitor your own water quality, don't just go by the LFS
I wouldn't have bioballs anywhere in the system. They aren't needed and in general the only end result is extra nitrate. Your live rock is about 80% of your filtration. The rest comes from a skimmer, fuge, and water changes depending on the exact system.
I don't know what Marine Pure is, but is sounds like either another gimmick or something that will work but only in a tank that is very close to ideal and just needs a subtle boost. I wouldn't recommend using it, at least not without some more information.