Habitat - Indoor :: Substrate Sand, Large Gravel or Both

[alexo52090]

I just bought a 180 gallon tank for my 2 turtles and bought about 100 pounds of grey slate for the bottom but i was thinking about putting sand down fist under neath the rock so it doesn't scratch the tank.
So 2 ?s
Does larger stone or gravel scratch up a tank?
And is there any major problems with using sand as substrate?

[vear]

There's a sticky on the subject of sand. You should take a look: http://www.redearslider.com/forum/viewtopic.php?t=17268