its called best play sand, bought it at toys r us, a guy from my local reef club said he had heard good things about it but couldnt remember the name, so i went and bouth a 50 lb bag today. when i did the vinager test it showed some tiny bubbles when the vinager came in contact with the sand but they didnt stay and float or anything. i guess you could say there was very minimal fizzing but is that all i am looking for?