Well, as the research I've read has put the blame of reef degradation to excess labile DOC aka Carbon Dosing, I certainly question the wisdom of adding any labile DOC to a system. Excess labile DOC can have acute effects on corals like the necrosis you mentioned but unfortunately it can also have chronic effects that may take years to eventually cause issues. And I gotta point out to have the correct Redfield ratio you need to be including particulate and organic forms of carbon, nitrogen and phosphorus. Just measuring inorganic forms of these three will certainly give a wrong ratio. And how old is the system you posted pictures of in your OP?
You do have spectacular looking corals, unfortunately we can't use colorful corals as an indicator of healthy corals. Neither can we use growth. So how are you determining your corals are healthy?
We know cryptic sponges are processing labile DOC 1000X times faster than the bacterioplankton in the water. How are you determining what's being processed by sponges and what's being processed by bacteria? Sponges also process the various forms of labile DOC differently and some can form feedback loops with algae detrimental to corals. How are you confirming the resultant compounds the sponges in your system are benefitting corals and are not detrimantal to them?
For an excellent introduction to the conflicting roles of DOC in reef ssytems I highly recommend Forest ROhwer's "Coral Reefs in the Microbial Seas" This video compliments Rohwer's book of the same title (Paper back is ~$20, Kindle is ~$10), both deal with the conflicting roles of the different types of DOC in reef ecosystems. While there is overlap bewteen his book and the video both have information not covered by the other and together give a broader view of the complex relationships found in reef ecosystems
SOme additional videos by researchers looking at microbes and sponges:
Changing Seas - Mysterious Microbes
Nitrogen cycling in hte coral holobiont
BActeria and Sponges
Maintenance of Coral Reef Health (refferences at the end)
For the issues of color being indicators of stress see post #59 in this thread:
I don' think so. If they were so stressed out they wouldn't grow well so I think that when we have good color and good growth, they are probably thriving. I think our lights don't actually mimic sunlight and that we now provide the right spectrum to support colorful corals, but not full...
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