AquaChek
AquaChek test strips, a Hach brand: what the Select Connect kit reads, and the handling rules that decide whether a strip result means anything.
Test kits
Before you buy AquaChek
A Hach brand, and the handling is most of the test
AquaChek is a Hach brand, run out of Colorado, which is the useful thing to know about it: the strips are made to a laboratory company's process control rather than a pool brand's.
Almost everything that goes wrong with a strip result goes wrong before the strip touches the water, and AquaChek's own guidance is specific about it. Follow the directions on that container — strips change between generations, and AquaChek names using an older kit's or another maker's directions as the most common cause of a wrong result. Keep the cap tight and keep wet fingers out of the bottle, because a strip cannot tell your fingertip from the pool. Store at room temperature in low humidity.
And do not use expired strips. There is an expiration date on the container, and AquaChek's position is that however well a bottle has been stored, strips past that date should be replaced rather than trusted. A strip that has gone off does not fail visibly; it just reads wrong.
The comparator outlives the strips
The Select Connect kit pairs strips with a 7-in-1 comparator holder, and refills are sold separately, so the holder is the part you keep. The colors printed on it are what every reading is judged against.
Which is a problem when the chart fades, and a chart that lives by the pool fades. AquaChek runs a replacement color chart request form on its site for the Select 7-in-1 comparator holder — worth knowing before replacing a whole kit because the readings have started to look off. Test kit options are compared here.