If you have none left from last year, you'll need to add some cya. Add enough slowly to the skimmer while the pump is running to get to an initial reading of 30. Then, don't retest, add more or backwash for a week to let it have enough time to dissolve. Until you start to get a cya reading, it is going to be hard to keep any chlorine in the pool. You'll need to test morning and evening and each time add enough to get back to about 5. After cya is in there, you'll be able to just test and dose in the evenings. In a 24 ft AG, one quart of 6% bleach will raise your cl between 1 - 1.5 ppm.

Hope this helps.