It was a while back, when i had another tank i established it, read up alot about sand which one to use. so i went to argos to get the childrens play sand. Lots of the fish were dying, the sand looked strange and not smooth, and i had problems trying to clean it too.
If you run it between your fingers it should feel smooth. It it feels sharp then that sand is not appropriate to use in your tank. Just advice for the future if you ever want to switch back!