So this made me go check out an old reef2reef thread on Redfield ratio (having to do with ratio of elements) and i came across this interesting post which, I think, gets to some of the issues brought up above. In general terms, higher alk levels can stimulate faster coral growth but, that faster growth can lead to some problems if there are not enough nutrients to support it fully - e.g. food (organic source) or elements in the water column (inorganic). I may be off base her but this seems to be the crux of the issue. The best solution would likely be a combination of bringing down the alk a bit (reduce your reactor output/raise chamber pH), increase specific coral feeding, and add some bioload. In theory, this would bring the growth rate down a bit so it doesn't outstrip nutrients, add organic food source for the coral and bring up the inorganic levels a bit as an alternate food source.
OK - that was my reader's digest version of a really complicated topic - not sure it helps.
Do you think (or know) that corals utilize there nutrients from a source other than the water column?Yes, they do utilize nutrients from a source other than the water column, they are animals and they preferably utilize nutrients from their food – zooplankton, bacteria, phytoplankton, organic particles. But in the same time they are capable to utilize non organic nutrients like NH4, NO3 and PO4 from water column using active transport via cell membranes (but if both – organic and inorganic nutrients are present corals will prefer organic nutrients from food).So in an ideal situation coral could survive in water containing zero nitrates and phosphates if there is enough food for corals. But in real world, even in healthy reefs this is not always the case (not even speaking about home reef tank) that’s why corals need some phosphates and nitrogen in form of NO3 (or preferably NH4) to be present in water to survive. In healthy reef this concentration of nutrients is enough to be as low as 0,02 for nitrates and less than .002 for phosphates, because there is plenty of diverse food for corals. We found with practice that in a reef tank we need about 10 times more nitrates and phosphates in water present (more than 0.2 ppm nitrates and about .03 ppm phosphates), because we simply cannot ensure enough quality food for corals.