Buy the smallest container of CYA that you can find. It may be called stabilizer or conditioner but if the ingredients say cyanuric acid or isocyanuric acid, it is the right stuff. You'll need about 2 lbs. for now. You can add it one of two ways. Either pour it slowly into the skimmer while the pump is running and leave your pump running 24/7 for the next 4 or 5 days while it is dissolving. Also, don't backwash during that time period or you'll blow the CYA right out and waste it. Or, you can put it into an old sock and hang it in front of a return jet. Give it a squeeze once in awhile to help it dissolve faster. This amount should get your CYA level to 35-40. If you decide later that you want it a little higher, you can always add more but if you overshoot now, there is no good way to get rid of it.

By the way -- you have a mighty big pump for that small pool!