I am just running a long-term trial with the supply of nutrients in our systems. In our ICP-testing, analyses showed a slow drop in iodine concentrations which reached the lowest iodine concentration of 34 ppb in one system in August of last year. Then I decided to increase the iodine supply which led to higher iodine concentration in our Tropic Marin product All-For-Reef (I am employee of Tropic Marin and I am doing the R & D). The increased iodine supply with All-For-Reef and iodide separately was the only change at that time and the last change I have made. It resulted in iodine concentrations between 66 and 100 ppb in our systems.
Octocorals showed the most positive reactions. Besides better polyp extension zooxanthellate gorgonians resumed axial growth (length growth of the branches). All octocorals showed much larger polyps, from Heliopora over Sinularia and Sarcophyton to gorgonians. Already years ago I noticed that Briareum had permanently retracted polyps, similar to yours (star polyps), which where extended after doubling the iodine dosing.
This time the Briareum asbestinum with upright branches had started to show even tissue necrosis and is showing polyp opening and healing and growth of tissue after increasing the iodine dosage.
For me it is no question any more and it is the best advice I can give. Keep iodine concentration at the natural level of ca. 60 ppb.
Also the phosphate concentrations are out of question for me. Concentrations below 0.1 ppm have more disadvantages than benefits. Corals, especially SPS, need higher phosphate concentrations than nuisance algae. If you want to stop algal growth with low phosphate concentrations your corals will stop growing long before the algae.