I just went back and re-read the whole thread and realized that you have a plaster pool, not a vinyl one. In that case, cal-hypo is fine, because your target CH in a plaster pool should be 200-400 anyway. My mistake, sorry!!

In a plaster pool, calcium is a much bigger issue if it's low than if it's high, because if the water doesn't contain enough calcium, it will leach it from the plaster, making it brittle.

So you're right, Ben's right (of course), and I'll slink out of this now.....

Janet