You can use any sand, though most people prefer aragonite based sand for the added buffering ability. It's expensive though. Atleast moreso than playsand from the hardware store.
My 30lb bag of aragonite costs me $30 at the LFS
. For comparison, a 50 lb bag of playsand probably costs $5 at Home Depot, but you lose the buffering ability.
There are some aragonite based playsands out there, but they are few and far between. Some people suggest taking vinegar with you to the hardware store and testing the sand there. If you drop some vinegar on the sand and it fizzes, it's aragonite based. If it doesn't fizz, it's likely silica based.
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