Your chlorine level is fine for a pool with no CYA -- read the Best Guess page in my signature.

To add CYA you can EITHER add stabilizer directly or you can use dichlor for awhile. I'll put links for both below. Do NOT buy dichlor locally except at Sams -- you'll need to become an EXPERT chemical label reader before you tackle that. Stabilizer is usually still unblended, but even that is changing, so be careful. Adding dichlor is easiest.

Ben

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+ If you need stabilizer, and have access to a Sams Club, buy their 24 pack of 1# bags of dichlor shock. Each bag will add about 7 ppm of chlorine, and about 6 ppm of stabilizer, per 10K gallons of water. Otherwise, order dichlor from Amazon:
Kem-Tek Dichlor 22 lbs
We do NOT recommend buying dichlor locally, otherwise, at least until you are an EXPERT reader of chemical labels. The chlorinating pool chemicals sold at Walmart, Kmart, Costco, and most other local stores are diluted blends, sometimes with copper and other products with bad side-effects.