Haven't heard of that before. Try this:

1. get a gallon jug of distilled water from Walmart (abt $1)
2. rinse BOTH your test cell AND your sample bottle with distilled, then empty.
3. refill BOTH full with distilled, then let them sit for 30 minutes or so.
4. empty them, and IMMEDIATELY proceed with collecting and testing pool water.
5. do NOT cap or shake your sample bottle. test within 5 minutes of collecting.