Confusing CYA readings

I have been using Ben's test kit for a while now and have had consitent CYA readings of around 80. Last couple of times I tested I am getting a CYA of 30. So I took a water sample to a local pool store and the report said my CYA is 80. What's going on?

I tried different water samples and even using a different reagent (from my new kit) - same results. I am leaning toward believing Ben's kit because I also find I have no chlorine after the pool sits all night. But I have about 5ppm Chlorine while the pump (and SWG) are operating. Sounds like low CYA doesn't it? I should be able to maintain chlorine overnight - right?

If my test results are correct, where did the CYA go? I put in about 9-10lbs of stabilizer (6 months ago) - into a 18K to 20K pool. My test kit was showing 80 then. CYA is hard to get rid of so I really should have a CYA of 80 now.

I'll try to get another pool store to test my water. Is there anyone else experiencing any test result difficulties? Could I be doing something wrong? Does the reagent go bad? Will the CYA test results be the same if I'm viewing the tube (black dot) inside the house as opposed to viwing in bright outdoor sunlight? What if its cloudy out?
Thanks
Mike in FL

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Originally Posted by mshumack

I am leaning toward believing Ben's kit because I also find I have no chlorine after the pool sits all night. But I have about 5ppm Chlorine while the pump (and SWG) are operating. Sounds like low CYA doesn't it? I should be able to maintain chlorine overnight - right?

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Actually if you are losing the chlorine at night - that would not be due to CYA - CYA protects against sunlight - and there is no sunlight at night. Sounds like you have organics in the pool using up chlorine at night.

As far as which to believe - I have the same problem as you - Ben's kit tests <20, and pool store tests at 40. I think it might be user error on my part. Are you testing in a brighter/lighter area than you were before?

I generally get a water sample early in the morning (before sun up) and take it inside to test. My kitchen lights are pretty bright but I think the instructions say to view the "dot" in outdoor light. I don't know if this is important - and I have not tried to verify whether or not this really matters - although it would be easy enough to do.
Thanks for your reply.