some more info
Q: I'm keeping my skimmer. When I add a scrubber, should I expect the skimmer to produce less foam?
A: Not really. Adding a scrubber does not remove any food (protein), and that's what skimmers remove... food.
Q: I have a fish-only tank with large fish, and I don't care about small food particles floating around in the water. Do I need a scrubber?
A: Maybe not. If you don't mind cleaning the nuisance algae off the glass (which is caused by Inorganic Nitrate and Inorganic Phosphate in the water), then a skimmer may be fine. But if you are trying to eliminate nuisance algae (and glass cleaning) then you'll need a scrubber in addition to a skimmer, because a scrubber removes Inorganic Nitrate and Inorganic Phosphate (which is what algae feeds on.)
Q: I've heard that going "skimmerless" is only for experienced aquarists.
A: That was correct before July 2008. But it is now known how to easily build and use a scrubber to do all your filtering for you (just like in the ocean). It is cheap, easy, and best of all there is no possible way for something to "go wrong" with a scrubber and have it kill your whole tank. So scrubbers actually are now the entry level (beginner friendly) way to start out, provided of course you can build one, or find a builder.
Q: How is a scrubber different from a skimmer?
A: Scrubbers remove Inorganic Nitrate, Inorganic Phosphate, ammonia, metals and CO2 from the water. (Inorganic Nitrate and Inorganic Phosphate are what cause nuisance algae to grow on your rocks and glass, and are what you measure with your test kits.) Skimmers remove Organics (protein/food) from the water. Both scrubbers and skimmers, however, add oxygen to the water. Scrubbers add more though, and can supersaturate the water with oxygen.
Q: How does a scrubber compare to GFO (granular ferric oxide) phosphate removers like RowaPhos and PhosBan?
A: GFO's remove phosphate, and they may lower the pH while doing it. And they are expensive to refill. Scrubbers remove phosphate, as well as nitrate, nitrite, ammonia, CO2 and metals, and do so while increasing the pH. And once built and installed, a scrubber does not need to be "refilled". Also, if a GFO bag or canister spills, or if you accidentally drop GFO into the water, it will go everywhere throughout your sump/pumps/tank. If you drop algae in the tank, it's no different from algae that's already floating in the tank.
Q: How does a scrubber compare to vodka (carbon) dosing?
A: Both remove nitrate and phosphate. Vodka, however, requires a skimmer to operate (to remove the bacteria that grows), and this skimmer thus also removes food from the water. Vodka also reduces the oxygen in the water (bacteria use it). Scrubbers don't require (and work best without) a skimmer, and add oxygen to the water. Lastly is the safety issue of vodka: If you carelessly pour it from a bottle, "just a few ounces too much" can kill your entire tank in a few hours. With a scrubber, there is nothing that can happen which would cause such a situation. Scrubbers cannot kill your tank under any situation.