Welcome to our forum.
Not to hijack a thread but can you bring in a water sample to ANY local dealer and have them analyze for free? The dealer I bought the tub from is quite a ways away from us.I would be buying all my chems from the local guy so at least he will be getting my money from the chem purchases.
One thing to consider is that you can go to a Big Box home store, to the plumbing section, and purchase one of those Omni filter housings- they are made to connect to your incoming water piping, but can easily be adapted to work on a garden hose.