I have pool sand in mine and we washed it out for say 5 minutes every half bucket full. We had the sand in the tank in about 30 minutes of washing and because the pool sand is a heavier sand (ie: my gravel vacuum sucks it up in the vac part, it doesn't get sucked down the tube), It cleared up very quickly (under an hour). I think a big part of sand is how fine/coarse is it, and how clear/dirty is it to begin with. So, my experience has been that pool sand was very easy to add and maintain. When I do 25% water changes, my tank is crystal clear within an hour I'd say.