Beach sand can contain some nasty things you don't want in your tank, i would advise against it. Metals, containments, etc...
If you have a home depot, go to one, in the garden area, they have two different type of play sand, brown & white. Their white sand is really white, wash it really good. It may be out of stock since garden is out of season right now.
Here's a pic of the stuff:
Pretty white stuff...