the pups are now in my 75 gallon tank with no gravel. They will be there till time to sell them which will be 3-4 wks from now. Mother is in my 240 gallon tank with smooth gravel. it doesnt bother her and as you can see didnt bother the mating process. As far as the whole sand vs. gravel thing. I think its matter of personel choice. My motoros are pretty large so the gravel doesnt bother them abit and they are use to it. It did seem to bother the pups for the whole 8-9 hrs they were in there with mom cause maybe the gravel was just too big maybe rough on there delicate underbellies. Dont knw but they seem to be adjusted to no gravel alot better.