Without stabilizer (CYA) sunlight will break the chlorine down quickly so you should definitely get some CYA right away. Don't forget it takes awhile for CYA to register so wait about 5 days to test.
It is also possible that you have something in the water consuming the chlorine. If you add your chlorine after sundown and re-test in the morning, that should help determine what the culprit is.
I would also suggest you get a drops based kit to get a more accurate reading. Some WalMarts have the HTH 5-way test which includes CYA.
Peter
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