Kervis,
My husband was a judge today in the Delaware Valley Science Fair.
He purposed the same idea as Vinny did. Have your daughter think up a question and then develop a hypothesis. For sixth grade you would probably have to limit the parameters. Maybe an example would be:
If I soaked in my hot tub for 1/2 hour and did not treat the tub with chlorine (sanitizer) it will become cloudy and unsafe for use in (1) day.
The experiment would be how long it takes the tub to show visible contamination without treatment. Using your Taylor tesk kit, you can measure the amount of chlorine present when the tub is perfectly clear and the amount when it begins to cloud.
Science teachers love when the child continues the experiment to answer the next question that would logically follow...in this case, like Vinny suggested, demonstrate how long it takes to clear up again and how much sanitizer was required.
Be sure to have her write her procedure in past tense. good luck, this sounds like fun!