Barry,
A lot of people simply repeat what they hear on forums, true or otherwise. Here are two things I hear a lot:
1. Black substrate becomes dirty and looks bad.
2. Black substrate cuts down a lot on reflected light.
I don't know if either are true, but based on my personal experience:
1. Black substrate becomes dirty. A lot of this has to do with water flow. Crap settles if there is not enough flow, common sense. BUT a lot also has to do with grain size. I use Caribsea Hawaiian Black. It has fine to semi course grains. The grain size allows mulm to fall down into it, and sand sifters like nassarius get the detritus, so Hawaiian Black looks better over time, IME, than say Nature's Ocean Black aragonite because the Nature's Ocean is very fine and does not let any waste down into it. I don't consider my black substrate any dirtier than my white.
2. Black substrate cuts down a lot on reflected light. Probably some, but is it enough to hurt coral growth? Not IME. How much light reflected off white substrate actually makes a beneficial contribution to coral growth anyways? Does it go all the way back tothe reflectors and get bounced back into the tank? Doubtful. Does it reflect onto the underside of corals and provide benefit? In nature, reefs are not close to sand anyways and there is very little, if any, reflectivity of sunlight from the base of corals back up onto the underside of corals, I would guess. Real reefs don't grow on crushed white aragonite substrates, they grow on top of old corals.
I think the decision should be based on what you think is the most aesthetically pleasing. I prefer white in my 210 SPS reef, but prefer the black in my chalice tank for the offset it gives the chalice colors.
Here are pics of my 100 gallon tank with Caribsea Hawaiian Black, set up for about 6 months. Flow is two Vortech MP40Ws, set to 50% power each.
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