Could part of 'new tank' issues relate to all of the new equipment releasing various toxins (for example, its well described that tin can be released from PVC plumbing, and that this significantly decreases as the tank ages). Could there be other minerals, metals, etc - that could be being released in levels that though they may not kill outright SPS, anemones, etc - but enough to make them do poorly - just food for thought?
I also believe that many organisms take up trace metals like tin, mercury, etc etc - when the number of animals is vastly higher than the concentration of the toxin - these do not necessarily 'damage' the organisms.
There's a few parts to this that could be separated to think about how plausible they are.
1) elevated toxins/trace elements/unnatural substances from new materials
2) are any of these above inhibitory concentrations / no-effect concentrations for important organisms to coral success?
3) are they depleted by exports and broken down by microbes in fairly short time?
The answer to 1) I think we'd agree is yes, that some newly manufactured components will introduce compounds or elements that are foreign to the system. Every new thing has a "new plastic" smell etc.
And 3) seems to be yes as well. This
article "Down the drain" gives a breakdown of the elements exported by skimmate, skimmer sludge, and macroalgae (table 2). It seems that in addition to biologically important elements like Fe, every trace element seems to be depleted by exports as well.
The sketchy part of the premise is 2) that these foreign substances are above "no effect" concentrations for the coral or other organisms relevant to vigorous coral growth.
I think this may be unknowable from reading and debate, but might not be easier to answer with a hobby experiment.
If someone got small (2-5 gallon) tanks, each stocked with some coral frags:
One gets new PVC pipes dropped in, new waterfall pump etc. whatever other new items we can think of that might release concerning substances. The other gets the same, but those other items have been previously "cured" in the sump of a large established system for a few weeks.
Mass the coral frags before and after a month or so. If each treatment got two small tanks each, I'd be persuaded by the results either way.