You can just use some triclor tabs for awhile. They contain cya in them. You can use them for awhile, but monitor your cya level. When you get around 40, you should then switch to just using bleach. They are also very acidic, so if you have low ph, you might not want to use them. Another option is to just buy some cya. It is sometimes called stabilizer or conditioner. Check the ingredient label, and if it says cyanuric acid or isocyanuric acid, that is the right stuff. You can usually find it at Walmart, Lowe's or Home Depot or at a pool store.