Hotsprings FreshWater settings calculates VERY low -0.9 CSI

[lagreca]

I just got a new to me, 2019 Hotsprings Flair hot tub. I'm not new to hot tubs, and have followed the Nitro bleach method before. However, this one has a SWG (Salt Water Generator) built in, and I was going to try to use it. When I follow the owners manual, and plug in all of the recommended values:

• Salt: 1750 ppm
• CH: 50 ppm
• TA: 80 ppm
• pH: 7.4
• Chlorine: 3 ppm

Into the calculator, I get a CSI of: -0.9

I read the CSI explanation page and it states:

Quote
"those with SWGs and very hard water may elect to keep their CSI slightly negative (0.0 to -0.3) to help prevent scale build-up on SWG cell plates."

It also says I shouldn't focus on a "perfect CSI", but a calculated -0.9 seems quite excessive and has me concerned. Am I missing something, or what values should I change from the factory recommended numbers?

 

[Texas Splash]

I suspect your tub is fiberglass/acrylic, therefore the principles of CSI (to protect plaster) do not apply. A low CSI is an advantage to preventing scale on the salt cell. You should be fine.

 

[Mdragger88]

You’re totally fine.
Those disposable cells will foul more quickly than advertised if ch goes over 75ppm.

I don’t see you mention cya. Recommended cya for covered hot tubs is 30/40 ppm.
Follow the FC/CYA Levels.

 

[lagreca]

I don’t see you mention cya. Recommended cya for covered hot tubs is 30/40 ppm.
Follow the FC/CYA Levels.

Thank you for the response. I didn't mention CYA because it will not see much sunlight, especially in the winter. But I'm planning on starting with dichlor and bringing the CYA up to around 20 ppm, and then letting the SWG take over and supplement with bleach, and MPS shock once a week.

 

[Mdragger88]

The cya recommendation isn’t only for protecting chlorine from the sun in this case. It is to moderate the harshness of the necessary adequate fc levels for people & equipment/surfaces (head rests, covers, etc.)
Its a bit hard to measure cya when it is below 30ppm.
The bather load in a spa is a feast and famine situation. If starting with an fc of 3 adding a couple of bathers for 30 minutes or so may have you below minimum or even zero which is a recipe for hot tub rash & other fun conditions.
Having cya 30/40 allows you to run higher target fc levels comfortably without risking falling too low during your dips.
For larger use cases (multiple people) you may need to supplement with liquid chlorine mid session.

Note that many people have sensitivity to mps & it skews the cc’s test unless the interference reagent is used.

Since monitoring cc’s is imperative to gauging the health of the water many choose to forgo mps, myself included.
One less thing like Forrest Gumps says lol.
Chlorine is both an oxidizer and a sanitizer.
While Mps is only an oxidizer.
Keeping adequate fc at all times should make scheduled prophylactic “shocks” unnecessary.