from an earlier post
CYA is stabilizer. Your test indicates you have virtually no stabilizer as well. 1.5 lbs should bring you to 40ppm and will help you hold chlorine during the day. It will take a few days for the stabilizer to be effective in your pool.
Go swimming. Lack of stabilizer will not hurt you. Get it at Lowe's/HD/WalMart.

You need to read all the "stickies" posted at the top of each forum. It will explain much of what you need to know...including muriatic acid.