Why does WaterGuru recommend a Calcium Hardness level of 400 ppm for my Saltwater chlorine generator pool?

For non saltwater chlorine generator pools, a level of 300 ppm for Calcium Hardness is recommended.  

For saltwater chlorine generator pools, WaterGuru recommends a higher 400 ppm Calcium Hardness level.  The reason is because the higher salt level in such pools, typically 3400 ppm, compared to the other pools at typically 1000-1500 ppm salt, results in a difference in the calcite saturation index of around 0.12 to 0.18,which compared to 300 ppm would need 395 to 454 ppm Calcium Hardness to balance.  

For this reason we recommend 400 ppm instead of 300 ppm.  We also set the pH target to 7.6 for saltwater chlorine generator pools instead of 7.5 for non-saltwater chlorine generator pools.  

The higher pH target also reduces carbon dioxide outgassing lessening pH rise.  Having a lower Total Alkalinity target helps with that as well.

What matters most is the saturation index as one can have higher pH and lower Calcium Hardness (or vice versa) resulting in the same saturation index.

A Calcium Hardness range of 200-400 is universally recommended although these recommendations typically do not account for saltwater pools:

• PHTA: https://www.phta.org/pub/?id=C2C6DCB4-1866-DAAC-99FB-F3F6E7B592FA
• Hayward: https://www.hayward.com/blog/post/pool-water-chemistry-101
• NPC: https://finestfinishpools.com/wp-content/uploads/2022/08/npc-pool-start-up-english.pdf