Samples while circulating requred?

[anonapersona]

I just ran a full test of the pool water and was surprised to see a much lower value for CYA than I expected. The pool has been off overnight, it was about 8 AM when we caught the sample.

question: what values would be expected to vary after the water has sat still for a long time? I might expect chlorine to drop near the surface in sunlight in quiet water, as well as overnight due to consumption. Would CYA vary as well? If not, then it is probably an error on my part -- this time I had someone to discuss it with and between us it may be that the uncertainty of the drop dissappearing was relieved and we ened up at a lower CYA value as a result.

Would pH or any other values be different across a quiet pool?

I have another question about algae but will make a new post on that. Thanks.

 

[JasonLion]

It is always best to have been running the pump for at least 30 minutes to an hour before taking a water sample for testing. That said, there shouldn't normally be any significant variation in the CYA level unless the pump has been off for weeks or you were just adding fill water.

FC levels vary rather significantly when the pump is off, both because of sunlight and because of localized algae growth. The PH can be different at the surface because of debris falling in the water. The other levels should be fairly uniform, unless you have been adding fill water or it has been raining, in which case the water might not be throughly mixed yet.