Originally Posted by CinBos
If white, what is not good about it? Just curious.
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No fish lives over a white substrate. Fish are coloured accordingly, dark on the upper side and lighter on the lower, so when viewed from above they tend to blend in to the dark substrate, and when viewed from below they blend in to the surface.
When placed over a white substrate, fish almost always get stressed. Their colours pale as a sign of this. And the brighter the tank overhead light, the worse this can get. Covering the substrate with lots of wood, plants, dry leaves can help. But I prefer starting with a dark substrate to begin with, it makes it much easier.
There is also the aesthetic issue with white. It becomes very obvious, and it does detract from the darker colours of fish and plants. Similar to a background that is bright, shiny or white. And all this does affect fish.
I decided to change my tanks over to play sand for two reasons. First, I wanted to give the fish their natural substrate [thinking here of my substrate fish primarily]. And then I chose play sand because it is identical in appearance to the sand in many Amazonian streams, and you can't get much more natural than that.