It is sometimes labeled as stabilizer or maybe conditioner. Check the label. If it says cyanuric or isocyanuric acid, that is the right stuff.

If you buy a kit, make sure you get something that has a FAS-DPD test in it. If they don't have something like a Taylor K-2006, consider order it through Amazon.com at this link because by doing so, the Pool Forum will get a donation. Take a look at this link:

http://www.poolforum.com/pf2/showthread.php?t=10006