well Iron and greens are already known. too much Iron will lead MAJOR algea outbreak, so I never dose it.
pottasium-Iodine-floride does wonders to blues and purples, I dose at night and when the light come on in the morning I see a big difference. ( I dose it once a week at most, mostly when I miss a water change). Overdosing this can turn yellows to green, reds to green too ! so I guess I have a bit too much Iodine !
SI, I have no Idea yet ! but gonna pick up a test after work to see the amount of SI in my tank right now. I'm also reading Randy's article on SI, to find more useful info.
and of course K+ on brightness of colors.
this change has made me want to try different elements now just to see their effects lol there are 70 of them