I would be careful when buying aquatic sand that claims to be "fit for freshwater aquariums". I recently decided to try some (spent almost $25) that claimed it was fit for freshwater. Before I bought the sand, I emailed the company and asked if it was safe for fresh water amphibians. I received a reply reassuring me that the sand in question was, indeed, safe for all freshwater animals, including amphibians.
Despite this assurance, I decided to let the aquatic sand (after thoroughly rinsing) sit in a bucket with water and see if it altered the water chemistry over time (since I've been having so many issues with substrate lately). Within two hours the pH of the water jumped from 7.6 to 8.6 and my tests couldn't even read the water hardness! Suffice to say, I was both relieved (for not having put it in Sushi's tank) and very angry. I'm currently emailing the company (CaribSea), trying to get them to change their labels, but I have yet to get any response from them.
Moral of my story: Don't risk it. Apparently companies are willing to lie in the name of profit, even if it means harming the very animals they're supposed to be providing for. You're better off saving time, frustration, and money by buying play sand :happy: