Posted: Sat Dec 18, 2010 4:37 pm Re: I am about to add Sand .
The silica sand (silicon dioxide is the most common mineral in the earth's crust) is fine, the issue with silica based sand is that it can leech phosphates into the water. Phosphates promote algae growth. A good filter and regular water maintenance makes this a non-issue. There are a ton of people on this forum using play sand. If you feel more comfortable buying aragonite calcium sand, by all means that will work as well... it just costs more...a lot more. A 30 lb bag of dry aragointe calcium sand from a pet store is $20 on sale, $30 regular price. I'm not sure what size tank you have, but my 75 gal took 50 lbs to cover the bottom with about 3/4" of substrate. A 50 lb bag of play sand was about $4. Calcium based sand will also very slowly dissolve into the water column over time where as silica sand will stay put.
Play sand is noted for being bad in reef aquariums. In reef setups, calcium based sand is needed as a buffer for corals. Silica based play sand is not recommended for reef setups, but is fine for turtles.
Silica sand occurs in nature... and turtles live natively in silica sand environments in the wild so it's fine for your tank.