How long to wait to retest after adding chemicals?

[JohnT]

For CYA, I'd wait at least three days. Chlorine and acid, I wait a few hours. May not be best accuracy, but it's close enough.

[Watermom]

For CYA, I'd wait a week. Or at the very least about 5 days. CYA dissolves very slowly in your filter. If you retest for it too soon, it may have not all dissolved and you think you need more. Then, you end up with too high of a reading and the only way to lower it is to do a partial drain. Better to be patient with it.

Watermom