Thanks guys. Just worried about the SWG and the heater (pentair MiniMax NT). Draining 1/2 of the pool and rebalancing frankly sounds cheaper and easier than replacing the heater and cheaper than replacing the salt cell. Admittedly, I have NO idea about how long it would take the elevated level of calcium to render either unusable. Haven't made up my mind yet, so just reviewing my 'options'.

As for rain water, I live in san diego, so not expecting much help there.