SPS dietary requirements

In ambient conditions on the reef (with wet bio mass of zooplankton ranging from 0.5-4 mg/L, bacteria 1.5-3 X 106 cells/mL, and DOM ranging from 0.5-2 mg of C/L ), as a rough average - scleractinian corals could compose their energy balance as follows: 60-70% via photosynthesis, 10-20% predation, and 10-20% by feeding on DOM and bacterioplankton (Sorokin 1995).

Clever little fellas are these corals, interesting for all those forum people who say all they feed their corals is light. Indirectly, they are also producing the bacterioplankton and DOC which makes up the balance of their diet.
Does make you wonder though, as long as you are feeding your fish well and providing light, what is the point of all those expensive fancy coral foods?

The problem is: Amounts, size, and timing.

The amounts fed to your fish are a small percentage of reef amounts. Probably 1 percent.

The size of fish waste is large particles; corals need small particles. Some corals need very small particles.

The timing of your feedings, and thus fish waste, is daytime. Corals eat most at night.

Then there is the more subtle difference of composition of dead-fish waste to live-reef pods. That's why scleractinian corals have stingers... to kill and eat live pods.

Lastly, remember that photosynthesis only provides energy (glucose); it does not provide any nitrogen and all, and thus cannot provide any growth at all.

There is an interesting article about bacteria populations in march 2011 Advanced Aquarist. Seems that unless you are deliberately dosing organic carbon sources such as vodka etc the levels of bacteria are much lower than on a natural reef, an average level there would be 1million per ml. On the heavily skimmed etc tanks the levels were 1/10 this level and even on the unskimmed, no gac etc tanks the levels were still lower.
Bearing in mind that corals I presume gain their nutrition from whatever source is available at the time, could it not be the case that with adequate light to provide their energy source via the zooanthellae, the nitrogen food source for growth could come from predation on bacteria.
I know I have gone on about dissolved organic carbon in various other threads, some people agree with me and others don't that too much is not a good thing, but assuming that scrubbers produce doc at a rate higher than a tank without a scrubber, this carbon is a natural source of carbon dosing which would enable the bacteria levels to rise to more natural levels, in turn providing adequate nitrogen foods for the corals, and in turn maintaining doc levels at reasonable levels. The pods being produced must also contribute to the nitrogen source, either directly or via their planktonic offspring.
This is a bit of a ramble so apologies for that but when you consider that zooplankton might only make up 10-20% of coral nutrition it should not be too difficult to make it up from other sources, such as bacteria, a nitrogen rich food source.
So taking adequate light as a given, to provide the corals with the bulk of the energy they need, you need your nitrogen engine for growth and tissue repair etc. As long as you provide enough food to keep your scrubber growing via consumption of nitrate and phosphate, it will do its bit by producing the doc needed to fuel the heterotrophic bacterial growth which your corals will then gladly consume.
Even though the nutrition available in an aquarium is undoubtedly lower than on a natural reef, it must be important to look at your livestock and think how much they could physically consume. Unless you have the luxury of a tank crammed with sps, the bulk of us I would imagine have just a few specimens and so the amount of food they ultimately require must be small. If you are feeding to the guidelines, that surely is more than enough to maintain scrubber growth, doc production and bacterial growth.
I recall santa saying elsewhere he fed 72 cubes a day at one point. What amount of livestock would be needed to physically consume that much food! Ramble over!

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corals I presume gain their nutrition from whatever source is available at the time

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Yes, whatever is available that minute. But averaged throughout the day, food particles are hugely plentiful.

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could it not be the case that with adequate light to provide their energy source via the zooanthellae, the nitrogen food source for growth could come from predation on bacteria.

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Yes bacteria are nitrogen, as are microbes, but the feeding percentage I mentioned was in addition to this. The studies were before Sorokin, and found an average of 1 pound of food particles consumed per 1 cubic meter of reef water per 24 hours. This was only what they caught in a net; it would be in addition to anything microcopic or dissolved.

Yes the scrubber provides lots of doc, but the amount of chlorophyll in a scrubbed tank per unit volume of water is lower than a reef; so the doc is going to be lower. I think I calculated that a 100g tank would need a standing stock of 1 pound of algae to be equivalent to a reef. So you would need four SM100's running at one, cleaning two at a time, while the other two remained full.

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I recall santa saying elsewhere he fed 72 cubes a day at one point. What amount of livestock would be needed to physically consume that much food!

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I did it for a few months (limited by only having two scrubbers), and the food particles were consumed within minutes of being dosed in. Then the polyps (and fish) had to wait another hour for the next dose. On a reef, they dont' have to wait; they eat the whole hour (especially at night).

Here are some quotes from that AA study:

Bacterial Counts in Reef Aquarium Water: Baseline Values and Modulation by Carbon Dosing, Protein Skimming, and Granular Activated Carbon Filtration ( http://www.advancedaquarist.com/2011/3/aafeature )

"The natural biological filtration, which starts with bacteria and other microbes, is remarkable in its capacity to remediate reef tank water of TOC, easily removing 50% or more of the post-feeding TOC increase in tank water."

"Many strains of marine bacteria have a preference for amino acids as sources of carbon, nitrogen, and energy, and require vitamins and other growth factors."

"Marine bacteria can sequester elements, such as potassium, within their cells at concentrations far in excess of the concentration of the element in their environment (Thompson & MacLeod, 1974). Such sequestration presents the possibility of some degree of elemental depletion in a marine aquarium by bacterial export via protein skimming."

"There are only negligible differences between the measured populations of bacteria in both marine and non-marine water samples."

"Bacterial counts from reef water in Hawaii, Micronesia, Key Largo, and the Northern Line Islands all converge on a span of bacteria populations in the 500K - 1500K/mL range or so."

"The aggressive husbandry practices included protein skimming, GAC filtration, and regular water changes, in an active effort to scrub the water of nutrients. The passive approach did not involve any of these procedures. Interestingly, the aquaria subjected to passive husbandry exhibited bacterial counts that fell within the range seen on authentic reefs; 200 - 1000K/mL. On the other hand, the tanks that "benefited" from careful attention to [aggressive] nutrient removal protocols displayed bacteria/mL counts that fell far short of these numbers; only 90-140K/mL."

"It is probably safe to conclude that the UV sterilizer does not have a significant effect on the bacteria population levels in the tank's water column."

"Actively purified aquaria have water column bacteria populations that are approximately 1/10th those of authentic healthy reefs."

"Unpurified aquaria have water column bacteria populations that are approximately the same as those of authentic healthy reefs."

"Bacteria growth is Carbon-limited in aquarium water.

"Addition of a carbon source [vodka, ie, DOC] to an active reef tank via a recommended schedule does not lead to any measurable increase in water column bacteria load. [The bacteria are consumed as fast as they can multiply]"

"GAC does not seem to be an effect method for removing bacteria from the water column of reef tanks."

"One message comes through clearly from all of these experiments, regardless of the starting bacteria/mL level; only a minor fraction (~ 28 - 39%) of the bacteria present are susceptible to extraction by bubbles."

"GAC (Granular Activated Carbon) filtration does not remove bacteria from the water column."

"Protein skimming (bubbles) removes approximately 30 - 40% of the bacteria in the water column of carbon-treated or organic rich water, but the remainder is not susceptible to bubble-based removal."

"Aquaria subjected to active filtration via skimming present water column bacteria populations that are approximately 1/10 of those observed on natural reefs."

"Our studies have shown that bacterial growth appears to be carbon limited in reef aquarium water."

It is a fascinating study and just goes to show that most of what goes on goes unseen. Just think it makes a nice little theory, feed your tank just enough to get good scrubber growth to produce the doc for the bacteria to eat to in turn feed the corals and the filter feeders. Why feed more than is necessary and risk excess nutrients etc
Would make an interesting experiment to compare a set up like this to one with high feeding levels.
Aquariums don't have the benefit of billions of gallons of seawater and vastly more microbial species to deal with the waste.