I realize that cyanuric levels don't drop in summer except by dilution. Is there something about winter conditions that causes it to break down? I drop the pool level for winter below the jets. Pool is usually full by spring. I test cyanuric a few days after I open the pool in spring and pump has run for a while. I get a reading of zero(couple of kits to doublecheck and also testing at pool store) so I add enough stabilizer to bring it up to 30 or so and don't test again until mid-summer. When I test at midsummer though the readings are high 60-70. I do not use stabilized chorine in the pool, neither dichlor nor trichlor(have a chlorinator, but haven't filled it for last few years). I tend to have green algae bloom problems when the water warms up by july.

I'm beginning to wonder if I am testing cyanuric too soon in the spring. Perhaps it doesn't break down over winter? Perhaps the spring rain water has not been mixed thoroughly enough with the remains of the previous year and I'm being mislead into believing I need stabilizer and therefore regularly overdosing in spring?