why top downs ?

[kien]

I vote for "light from above". If you inspect your corals and look at the parts where the light doesn't hit it directly (like a shaded side or the base of a branching colony), the colours aren't that great at all. At least that's the case for my corals. They go from amazing from the top, to pretty good/okay on the sides to dull and possibly brown at the bottom (undersides of branches, base of colony, side of coral not getting direct light). Anyway, that's what I notice with my corals.