In my experience, change has a LOT more to do with with this sort of thing than elevated nutrients or anything else. Change might be a change in lighting, a major change in alkalinity, nitrate, or phosphate, a change caused by adding various trace elements or even stopping the addition of those trace elements, some unknown chemical introduced... any number of things. Too many people have successful tanks at elevated nitrate/phosphate levels and too many people are plagued with dinos due to extremely low levels of nitrate/phosphate, for that alone to be the culprit of GHA, cyano, and other nuisance outbreaks.
In my experience, short-term fixes are way more effective when everything else in the tank has become stable. For instance over the last several months, I fought an alk/Ca battle due to my tank's uptake becoming significantly more than kalk and my regular additions of sodium bicarb and Ca chloride could manage. I was waiting on a whiz-bang Ca reactor I had ordered last summer that never materialized. I finally punted and got a different Ca reactor. The result was some lost corals and a blue-green cyano outbreak. Once I got alk/Ca stabilized, I tested nitrate/phosphate and found that my phosphate was where I like it (around .1 ppm), but my nitrate had plummeted to <1 ppm, very possibly 0 as that is within the margin of error for the test kit. I like to keep my nitrate around 10 ppm. I dosed nitrate (Seachem Flourish Nitrogen) to hold me over and then ran Chemiclean two days before my next w/c, which was like 8-9 days later. True, it has only been 1 week since that w/c and adding carbon to remove the Chemiclean, but no blue-green cyano has returned. I will test nitrate/phosphate in a couple of days and will continue testing alk/Ca. I will adjust if anything is way out of wack and if blue-green cyano comes back, I will dose Chemiclean again. I already know that I'm in better shape than I was, knowing how fast the blue-green cyano came back after manual removal.
One other thing in regards to blackouts, for me they always created nitrate/phosphate and alkalinity spikes, and also lowered pH from where it normally runs. Therefore, I stopped using because I felt like the positive results were short-lived as the instability the blackouts created just put me back in the same place.
