At the beginning of the softening cycle, sodium ions occupy the resin's exchange sites. As water passes through it, the resin's stronger attraction for the hardness ions causes it to take on the hardness ions and give up its sodium ions. Iron and manganese are considered hardness and they are removed also, provided they are in solution. Ion exchange cannot remove suspended matter.
As water flows downward through the resin bed, the resin at the top of the bed gives up its sodium first. The exchange process is not instantaneous, so exchange occurs in a band called a "reaction zone". The reaction zone's depth depends on incoming water hardness and TDS, flow rate, water temperature and resin particle size. When the reaction zone's leading edge reaches the bottom of the resin bed and hardness passed into the service line, the resin has become "exhausted" and it must be regenerated before it can remove hardness again.
The regeneration cycle starts with backwash, an upward flow that loosens the resin bed and flushes out suspended particles. Backwash usually lasts about 10 minutes.
Regeneration occurs when a solution of sodium chloride (salt) brine is passed through the resin in a downward direction. An eductor draws concentrated brine from a storage tank and dilutes it to the right concentration. Brine draws lasts from 10 to 30 minutes depending on salt dosage (weight of salt per volume of resin). A large excess of sodium ions causes the resin to release its hold on hardness ions picked up during the preceding service cycle and returns the resin to its sodium state.
Excerpt taken from here:
http://www.culliganmiami.com/pf7.html
I'm still in the beginning stages of learning chemistry but my take on it is this:
Chemi pure starts out with a saturated sodium state. Submersing the media into an (and I qoute boomer) "85% table salt" solution saturates the media causing it to re-release everything that has been taken up including ammonia, etc. To the SW hobbyist it is useless since the media never has a chance to absorb ammonia, metals, etc before becoming over-saturated.
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