This is related..
Many people have trouble using carbon, and try adding on a scrubber to fix it. It's better however if you just start with scrubber-only if you want scrubber-only. If you want low nutrients, it depends on how good you build and run your scrubber, and if you have other filters. Any type of scrubber can get numbers to "zero" on regular test kits once the tank has cycled, if that is your goal. Algae is algae, and photosynthesis is photosynthesis. There just has to be enough of it at all times. Photosynthesis = Light x area x attachment x air/water interface turbulence.
If that is your goal, and if there are no other filters or water changes, then you'll want multiple scrubbers so that at least one is always filtering when you clean the other. When algae is the only filter, nutrients shoot up real quick when the filter stops.
Adding carbon changes the control of what gets the low numbers. The carbon will usually win if run strong enough, and will really slow down the algae. So they sort of fight each other. Same with GFO. The only carbon that gets into real reef water is from algae (glucose), so real reef water does not have to deal with extra carbon being added. All the filtering there is done by photosynthesis. Here is a comparison of algae scrubbers to carbon dosing (vodka, pellets, etc)...
Carbon dosing does not:
Remove metals.
Increase pH (dosing actually decreases).
Increase oxygen (dosing actually uses oxygen).
Remove CO2 (dosing actually adds CO2).
Work well without a skimmer.
Grow pods.
Provide any reverse photo-period pH stabilization.
Which of course means that scrubbers:
Remove metals, including copper and heavy metals.
Increase pH, usually by 0.1 or 0.2 pH per scrubber.
Increase oxygen directly by photosynthesis, and indirectly by bubbles or flowing water.
Remove CO2.
Do not require a skimmer, doser, or anything other equipment (an upflow version does not even need a water pump).
Grows tons of copepods (in saltwater), and even amphipods if you don't use freshwater to clean.
Can be set to reverse photo-period of the display.
Scrubbers also add trace elements (all organic traces in the ocean come from algae) including Vitamin C, Amino Acids, and Carbs (these come from algae in the ocean too).
Scrubbers also cannot over-dose, and they can't over-scrub. And if the scrubber is an upflow version, then it can't even dry out if the power goes out.
But probably the biggest advantage is that a tank can be set up to be scrubber-only, with no other equipment, and no water changes.
However let's not forget the fun part: You can take some of the algae from the scrubber and feed it your fish!
