Skimmers will remove dissolved organics before they release nitrates and phosphates. Macro algae will remove nitrates and phosphates. Think of them as stage 1 and stage 2 filters. Remember, a little of this filth is good, its a nice treat for your corals. Anyways it all really depends on your bio-load. I run both currently. I have a 75 gallon with 9 fish including 2 tangs
. My nutrients are way too low. My fish are fat. I over feed them, I overfeed my corals and my phosphates and nitrates don't have a pulse. I have recently pruned my chaeto down to the size of a tennis ball in hopes to get a reading of either. If that doesn't work, I'll have to consider running the skimmer for a lesser time or just open up the skim cup plug completely. This way it's doing nothing but adding O2 into the tank.