When I defoliated my 125g discus tank I went to bare bottom for about a month. All my discus are adult. With no substrate, they were assuming a slightly tilted position all the time, I guess due to seeing their reflections, so I put about 1/2" of pool filter sand on the bottom and they love it. It's really cool to see them "blow" into the sand looking for food. The live blackworms crawl down into the sand leaving abot 1/2" of body sticking out, looking like red grass. The discus pick them off easily. I find that the sand bottom isn't any harder to keep clean than bb because it's such a thin layer.
Mark
Mark