If you're lucky enough, many types of playsand are aragonite and quite cheap. Might be sparse at this time a year though, better availability in the summer, check at HD
or other similar large chain stores. You can test the sand for aragonite with regular white table vinegar. Place a small amount of sand in a bowl and add a few tblspn of vinegar. If the sand fizzles, it's aragonite. If not it's silica. Ooltic is just a fancy word for small round and calcerous which is prefered in a marine set up over that of silica which is flat, sharp edged and inert.
If you cannot find the aragonite cheaply at the hardware stores, the LFS
will most definately have it as will e-tailers. Just stick with the dry stuff, not the wet "waste of money" products. My personal preference is Caribsea's Aragamax select.