A K-2006 from Amazon or a TF-100 from
TFTestkits.net. Either one will be fine.
TFP does not trust pool store testing as it is often inaccurate and the ad vice based on it is often dead wrong. It is our contention that the pool owner is the only one that truly cares about their pool. Everyone else is simply trying to make money off of it. You'll notice that many times pool store testing is often accompanied with a print out of the corrective actions you need to take and a list of chemicals you need to buy. The chemicals are often more expensive versions of stuff you can find in your local supermarket, big box store or hardware store. The tests always tell you something is wrong and always instruct you to buy overpriced pool store chemicals.
When you test your own pool water yourself, you then know exactly what your pool needs and you can come here for the very best advice....for free!