Acceptable overnight FC loss and testing error margins

[saraiks]

While trying to test for FC loss overnight what should be an acceptable number ?

I have tested to a 0 ppm to 2 ppm drop overnight without any other issues.

Can this be considered within the error margin of the test ?

 

[JasonLion]

The FAS-DPD test is +- 0.5 on each test. So a difference of 1 ppm is within the error range of the test and can be ignored. It isn't that difficult for there to be 1 ppm of chlorine lost to pollen or leaves falling in the pool. Both of those together could account for a difference of 2 ppm. Still, if watching FC overnight to decide when to stop shocking I would still go an extra day if the difference was more than 1 ppm. It is better to be sure you have gotten all the algae.