I asked the manufacturer of the "dutch synthetic reefing" method his opinion on ATS systems. He explained algae releases compounds that may affect sps corals. Apart from that, he has never seen an sps dominated aquarium do really well with an ATS-only system. Apart from that, Julian Sprung recently released this video; I wonder to what extend algae does release compounds, if so, which compounds? And to what extends are these compounds harmfull?
Reefs vs tanks is always a completely different set of circumstances. I don’t have the answer and I’m not sure anyone really does really. But there’s some truth to this I feel, to some extent. The blanket statement about never seeing a successful SPS dominant reef tank when running an ATS is mainly, IMO, not searching hard enough quite honestly. Also remember, the algae scrubber really only recently has started to gain traction and become acceptable in the mainstream. Thee are still parts of the US where if you bring up Algae Scrubbers in a group/club they’ll tear you up and down....so it’s still got a ways to go You can easily offset nearly any potential exudate or chemical interaction issue by adding a very small amount of carbon to the system, and changing it regularly. By small amount, for instance, in a 75g system, 1/2 cup in a media bag sitting in the sump in the flow pathway is plenty. Change maybe once a week. Not a full reactor or anything. There’s definitely more to this whole story, that’s for sure. But a lot of it is just educated guessing. Err on the side of caution if you feel it necessary and run some carbon if you keep SPS. That’s actually what I have been recommending for a while now - for heavy SPS + scrubber, use either a small skimmer or carbon, or both. No worries then
>>>I wonder to what extend algae does release compounds, if so, which compounds? And to what extends are these compounds harmfull?<<< Many organisms living in the ocean, including corals, release substances that can potentially be detrimental to other organisms. One aspect of this discussed more regularly on forums now is algae allelopathy and its negative affect on corals (allelopathy is the chemical inhibition of one plant (or other organism) by another, due to the release into the environment of substances acting as germination or growth inhibitors). Basically, there are a few specific sugars produced in the exudates of photosynthesising organisms that are utilised by certain strains of virulent bacteria. The exudate of larger, fleshy algae typically contain a higher percentage of sugars, in general, than other photosynthesising organisms, and also produce greater quantities of exudate. Some algae species produce these specific sugars. Now on a healthy reef, everything has a purpose. But, in circumstances where, for example, nutrient run-off from land, and/or, disease or over fishing has resulted in the decline of population, or diversity of, algae grazing fish & invertebrates, algae biomass has been able to increase significantly. This leads to an increase in the volume of specific sugars exuded, and that leads to populations of virulent bacteria increasing. These virulent bacteria now exist in large enough populations to interfere, one way or another, in the healthy functioning of the coral holobiont, causing death. This is the main point; these chemicals only become a problem where external forces allow algae biomass to increase well above the levels found on a healthy reef. Much of the problem is also due to the algae being in very close proximity to, and/or, coming into physical contact with the coral. Now the question is; does the algae species growing on your scrubber screen produce these specific sugars that promote virulent bacteria that may be detrimental to corals? Even if the answer is yes, is the volume of algae growing on a scrubber screen equivalent to, less than or greater than the typical algae biomass growing on a healthy reef? I would say, less than.
