As little or as much as you want... as long as it's not blowing the fish around. I put a powerhead in my 150g mbuna tank for a while, but my two canisters were plenty of flow, so I took it back out. And, there's really no need IMO to put cichlid salt in the tank. Some people want to so it buffers up the water and adds the minerals to make it very malawi-like... but I just put prime in my water. These fish aren't wild caught fish, they're bred in farms just like 90% of the other fish we keep. Unless you get wild caught of course.