1. Order the Taylor kit; using successive dilutions with distilled water, I validated it against the AquaCheck kit, and they correlated well at the lower levels. I'm guessing the Natural Chemistry kit is bogus. Remember, they'll sell more if it consistently reads high! http://pool9.net/tk/.

Tip: get some sticky putty (Scotch brand @ Walmart) to hold the Taylor test cylinder. It's really tall and easy to tip over. A bit of sticky putty to set it on will make the test go much more smoothly. And use a TIMER for the wait period -- otherwise it's too easy to get impatient.

Regarding the powder - I haven't re-read the whole thread: did we ever suggest, or did you ever do the DE test? It would confirm or eliminate the filter as a source of problems. Plus, if you hand vacuumed the powder while DE was in the filter, you could be sure of capturing the dirt. And, if there is live algae in the pool, it will tend to rapidly stop up the DE and thus your filter, giving another indication. http://pool9.net/de-test/