I used pool filter sand in mine. It's heavier than play sand. I did the 5 gallon rinse method, although I think I could have got away with not rinsing at all. Pool filter sand is pure silica sand. Rememeber when filling any tank with sand like substrate to turn off filters, some ppl put an upside down plate on the sand and use it to break the force of the water from hitting the sand directly. Here's a link w/ pictures of the 5 gallon bucket rinse method....http://www.cichlid-forum.com/articles/cleaning_sand.php