I just read Dr Helmenstine's article on water hardness/softness. She obviously understands the subject, so perhaps I've finally found a forum that can answer my question! Spa care forums have been of no help so far.
My house is in Southern Maryland, St Mary's County, and we have our own well. When we moved from PA 13 years ago, one of the first things we noticed is the "slimy water" syndrome, which I eventually learned is due to the water being too soft. We can live with the slimy water, but there are two other problems it brings.
First (a minor inconvenience) is that I CANNOT properly cook spaghetti! As it boils, it seems to abruptly go from uncooked to mush. So we buy bottled spring water from the store, adding a couple of dollars to the cost of our meal.
The big problem is our hot tub. We've gone through hell trying to learn how to balance the water, but we've learned a thing or two in the process - and raised even more questions. The most obvious thing is that the pH is quite high, so we have to dump large amounts of pH-Down into the tub. But then we find that the "calcium hardness" is extremely low, near zero. So we have to dump in calcium, which has to be counter-acted with even more pH-Down.
Now, I'm puzzled how the pH can be so high when there's virtually no calcium in the water. No tests we've done or had done indicate what chemical makes the water so alkaline. A more comprehensive test is very expensive, so we haven't done it. Can anyone make a guess as to what it might be? And, is it possible to remove it?
Another problem is that my spa's pump shaft seals don't last very long. I notice that there is either some erosion of the graphite ring, or it may be a buildup that makes a bumpy surface - it's hard to tell. We've been using Baqua sanitizer, which some people claim is hard on seals, but I have to wonder if it's only my strange water.
Btw, I found that pool filling services around here get their water from the same aquifer as ours! So unless there's some sort of filter or coagulator out there that could fix the water, the only solution would be distillation, which I'm sure would be very expensive.