Either will do if in place of rock
nobody has real control over denitrification via media in an aerobic filter, it happens rarely not by direct control.
its only lucked upon, nobody has a way to actually arrange sand or filtration material to denitrify although actual nitrate removing media isn’t hard to come by. Denitrifcation outside of a dedicated reactor (that’s an aerobic filter they’re in above) is a made up sales lark in reefing, feel free to use either option, the effect will be nitrification.
remember denitrifications history in reefing: since the nineties we were all told mere live rock reduces nitrate bs produces it, and we were told any deep sand bed would reduce nitrate
those two statements turned out false we can see in forum posts