I'm no expert like alot of the replies you'll get.....but I researched that same question recently, and read that while play ground sand would work, it is very fine and easily disturbed in your tank...I used pool filter sand which was inexpensive (less than $10) at my local pool supply store. It may be a little bit larger granules and heavier, which should work a little better.
Regardless of the sand you choose, be sure to rinse it thoroughly prior to putting it in your tank. I thought I had rinsed mine well and my tank was still cloudy for 2-3 days while it settled......if I could do it again, I'd put some in a 5 gallon bucket and stick the garden hose down in there....move it around alot and let it overflow the cloudy water out until it's clear....I did this but in a much smaller bucket :-(
Good luck!!
Sent from my SM-N900T using Aquarium Advice mobile app