snails are fine with sand, the MTS are the most common snail for sand tanks as they dig under it.in my gravel tank, its about 1inch think all across, as its difficult to clean because the gravel vac had to be pushed into the gravel to suck up the crap.i also personally think you have too much gravel, but its your choice. ive recently swaped gravel for sand in another tank, it looks more natural and i think my ottom dwellers will like it more. i havent cleaned it yet, but i will try holding the vacumm just above the sand.its a personaly prefrence to what you have in your own tank, gravel and sand both have pros and cons, it depends on what fish and what techniques you are using.both look great to me.