nice detailing of light impacts~ the debate about algae causes and fixes will rage on forever...but lately ive come to see algae, including your scenario, in a fully different light than how causatives were taught to me when I started reefing
there is no problem with your nutrients even without test kit data, even factoring in if you were a little above po4 targets. a nutrient problem causes you to have coral growth issues, zooxanthellae density + and darkening, calcification issues but low level algae growth doesn't always mean nutrient problems.
we can search up neat studies that show how algae will grow on pristine, non eutrophic reefs just by the researchers boxing off parts of the reef with grids so that grazing animals can't get to the substrate. these algae find a way
details:
see how the glass doesn't have the growths...waterborne nutrient issues contact all surfaces/so it follows if this was a po4 thing the algae would be as much all over the tank, but its on the reef substrates where it belongs, is adapted to, and is awaiting the beak of a parrotfish to rasp it off only so that it can grow back still in pristine param conditions.
I now will forever see nutrients as something you set a target goal at, its never in response to an invasion, and once you attain that target param goal for nitrates or po4 then you no longer have nutrients as a causative for any invasion, purposeful farming in absence of the right grazer match will be the enduring cause after nutrients are in balance.
your corals don't want to be stripped more, they'll bleach. You can see from the pics your balance is already set, can't rip anymore po4 as its not the problem anyway, OR those studies would simply have no algae growing under the grid blocks even without grazer help.
We get the pages+pages of tank fixes in the peroxide thread in your exact conditions by just cheating and burning off all the algae with peroxide, your turnaround time would be about 4 days to clean/no algae.
some use grazer experiments to ward off the algae that still gets past ideal conditions, either way is fine but im sure you shouldn't attack water any more, hold course and attack the algae directly and you wont have the issue with either light. no one says have to do your whole tank
lift out a test rock and apply only to target, let sit, rinse put back in and compare that to non treated areas in 3 days, algae w simply be gone. one option of many for the direct removal option. the ideal params you have work better for growback prevention, not for target removal, that's why you still have algae in spite of nice params.
