I plan to switch from gravel to sand and I'm gonna do a cichlid tank, so I'm gonna be using aragonite, but my question is do I still have to use water conditioner or does the aragonite condition the water?
What kind of water conditioner? Dechlorinator you still have to use. The aragonite will help buffer the pH so it is lower for African cichlids.
Generally, aside from dechlorinator you really don't want to use anything else to adjust the water chemistry - the fish will adjust to your water where it is better than if the parameters are swinging around with supplements and such.