One of the big benefits of a scrubber is that it keeps food in the water. Here is an update pertaining to this:
Part 1 of 7:
Taken from "Reef Food" by Eric Borneman: Reef Food by Eric Borneman - Reefkeeping.com
"Detritus, marine snow, particulate organic material, and suspended particulate matter are all names for the bits of "dirt" [food] that flow around the reef; material that is composed of fecal material, borings, algae, plant material, mucus, associated bacteria, cyanobacteria and other particles. Decomposers (mainly bacteria and associated flora and fauna) break down waste material in the water, on the reef, and primarily, in the soft sediments. The result of their presence and action is not only a food source in and of itself, but provides raw material for channeling back into the food chain, largely through the benthic algae and phytoplankton.
"Phytoplankton [food] are small unicellular algae, or protists, that drift in the water column. They may be very abundant in and around coral reefs, and they are capable of absorbing large amounts of organic and inorganic nutrients. [...] Some of the reef animals can feed directly on phytoplankton; many soft corals, some sponges, almost all clams, feather-duster worms, and other filter feeders utilize phytoplankton directly as a food source. Small animals in the water column, termed zooplankton [food], also utilize phytoplankton as a food source. For the smaller zooplankton, phytoplankton and bacteria are the primary food source.
"Both of the [photos not shown] are from reefs on the Great Barrier Reef, Australia. The left photo shows the clear "nutrient poor" (oligotrophic) waters of the outer reefs. The right photo is of an inshore "nutrient rich" lagoon reef off Townsville. Notice how coral coverage in both systems is high, and even though the green phytoplankton-filled lagoonal reef is nutrient rich, it supports a high density of Acropora.
"Coral reef food sources, then, are largely produced by the ocean. Bacteria, detritus, phytoplankton, zooplankton, small benthic fauna, mucus, and dissolved organic and inorganic material of various types and sizes are what comprise the majority of food on a coral reef.
"In aquaria, we are faced with several realities. Our phytoplankton and zooplankton populations are generally negligible to non-existent in comparison with coral reef communities. Those which do exist are either rapidly consumed without having a chance to reproduce, or they are rapidly removed or killed by pumps and filtering devices or suspension-feeders. Coral mucus, bacteria, detritus, larval benthos and other "psuedo-plankton" might be present in a reasonable amount if the water column were not stripped. On the other hand, dissolved organic and inorganic material [nitrate, phosphate] levels are frequently much higher than they are in the ocean. [...] Even very well maintained aquaria are generally found with much higher levels of nitrogen and phosphorous than wild communities. Even though many desirable organisms are able to utilize these nutrients, levels in most aquaria are very unnatural, and coral reefs under such conditions often wane or die - a process known as eutrophication.
"It is the lack of water column-based food that results in limited success with the maintenance of some desirable animals, such as crinoids, flame scallops, clams, certain corals, sponges, bryozoans, and many other invertebrates. Even the symbiotic (zooxanthellate) corals [like SPS] suffer, despite many obvious long-term successes with these animals.
"In terms of previously mentioned export mechanisms, it really does little good to be cultivating or adding more food material in the water column if it is all being rapidly removed by filtration devices. Live rock and sand provide abundant filtration, and some of the articles in past issues describing the set-up and use of unskimmed tanks are, in my experience, something that should be seriously considered. Algae Turf Scrubbers are also viable systems that provide low ambient water nutrient levels [of nitrate and phosphate] while maintaining higher amounts of food and particulate matter in the water. I also feel that if protein skimmers are used, they should probably be used in an intermittent fashion.