Why would you need to get to the bottom of the tank with sand? All the crap stays on top rather than sinking in, which is why it's so much easier to clean in my opinion. No digging around in it to make sure you've gotten everything.
Its been my experience that after a couple of years in a large tank the bottom of the sand turns black and smells like sewer! Believe it or not sediment will sift through the sand over time to the bottom. Now I havent used sand in over 15 years and the filtration is much better now a days so it may not be that way now but it sure was 20 years ago.
That's why you're supposed to stir your sand on occasion! That's the work of anaerobic bacteria; the sand becomes compacted and oxygen cannot reach the bottom layers for aerobic respiration to take place. I can see why you'd prefer gravel if you don't like the idea of having to stir sand, but personally I'd much rather stir sand once a month than have to vaccuum gravel. That's a royal pain in the arseIts been my experience that after a couple of years in a large tank the bottom of the sand turns black and smells like sewer! Believe it or not sediment will sift through the sand over time to the bottom. Now I havent used sand in over 15 years and the filtration is much better now a days so it may not be that way now but it sure was 20 years ago.
I will have to give you that one. I never knew you were supposed to stir the sand monthly, so in all actuallity one is about as bad as the other in my opinion. I will admit I love the look of sand in a tank and now that I know your supposed to stir it I may try it again on one tank. Going with out any substrate would be ideal but Im not sure Id like the looks of it.That's why you're supposed to stir your sand on occasion! That's the work of anaerobic bacteria; the sand becomes compacted and oxygen cannot reach the bottom layers for aerobic respiration to take place. I can see why you'd prefer gravel if you don't like the idea of having to stir sand, but personally I'd much rather stir sand once a month than have to vaccuum gravel. That's a royal pain in the arseIts been my experience that after a couple of years in a large tank the bottom of the sand turns black and smells like sewer! Believe it or not sediment will sift through the sand over time to the bottom. Now I havent used sand in over 15 years and the filtration is much better now a days so it may not be that way now but it sure was 20 years ago.
Jimmy B) 
If your sand bed doesn't get stirred around every so often (either by you or critters in your tank,) areas of it can become compacted and oxygen cannot reach them. In this situation, anaerobic bacteria that don't need oxygen to survive grow in the sand bed. The hydrogen sulfide gas they produce is what gives the sand bed its bad odor, and the sand also gets stained a dark colour, though chemistry isn't my cup of tea so I can't tell you exactly why that is
