What Salt/TDS values to use for CSI calculation?

[Strategerizer]

Can someone provide guidance on correct Salt vs TDS inputs when calculating CSI?

I replastered my pool and added salt. I measure using use Taylor salt kit and HM TDS-3 probe. My AquaRite cell is old/bad so I am not trusting that measurement. Here are my conditions:

• Pool fill water (sample taken from water hose) from the hose
  Salt = 400 (Taylor kit), TDS = 400 (TDS-3 probe) - is there so much salt in city water?
• Pool water 3 weeks after fillup, towards end of "start-up" (no salt added yet)
  Salt = 800 (Taylor kit), TDS = 620 (TDS-3 probe) - no idea where the extra salt coming from, do pool chemicals added have salt?
• Pool water after adding salt (6 x 40 lbs. salt in 13,000 gal. pool, measured several weeks after mixing)
  Salt = 3100 (Taylor kit), TDS = 3040 (TDS-3 probe)

I am confused on which numbers to trust and what numbers to enter in CSI calculations. I expect TDS probe number to be larger than Taylor, assuming Taylor measures only salt and TDS measures salt + all other minerals in water. I assume I can trust Taylor accuracy more and that maybe TDS probe needs to be recalibrated? Can I just use the number from Taylor?

Also puzzled about the salt/TDS levels from the water hose - so all/most TDS from my city water is coming from salt? And then how come 3 weeks after filling up the pool the salt levels increased? I can see how TDS may increase from various chemicals put in water but why would salt levels increase?

New salt cell from CircuPool wants salt levels between 2700-3400; what level should I shoot for and what measurement (Taylor vs. TDS-3) should I rely on?

I appreciate any input/explanations...

Thanks!

 

[ajw22]

Rely on the Taylor K-1766 salt test. It never loses calibration.

Use the Taylor K-1766 salt measurement in PoolMath for the CSI.

Aim for 3000-3200 ppm for your SWG.

All forms of chlorine you add to your pool add salt as well as muriatic acid.

Salt - Further Reading

www.troublefreepool.com

 

[JoyfulNoise]

Use the Taylor K-1766 to get your salinity set. It measures chloride ion concentration directly and has no other interference. Your TDS probe measures anything that will conduct electricity in the water so it will always just be an inference. Yes, municipal water supplies can have as much as 500ppm chloride ion in them. It’s not good to run that high but it’s also a cost/benefit calculation and the cost of lowering the chloride content may not be worth it to the municipal supplier. There’s lots of elements contributing to the TDS of municipal water, not just sodium chloride.

For the PoolMath App you use salinity value from the K-1766. PoolMath does the rest.

 

[Strategerizer]

That's great - thanks so much for your expertise and helpful input.

@ajw22, if chlorine and acid introduce salt, should I expect my salt levels to add up over time? (Since salt does not evaporate and loss will be only from splash-outs)

 

[ajw22]

@ajw22, if chlorine and acid introduce salt, should I expect my salt levels to add up over time? (Since salt does not evaporate and loss will be only from splash-outs)

You will not be adding chlorine with its salt now that you have your SWG going.

MA will add some salt but it will not be material with the salinity you now have for the SWG.

Always test the salinity with the K-1766 before adding salt to the pool.

 

[Strategerizer]

@ajw22, makes perfect sense - thank you!

 

[Strategerizer]

I have a SWG pool and plan on adding Borates. SWG makes keeps my pH range on the high side. I know the TFP's recommended min and target levels of Chlorine at different CYA levels :

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.

www.troublefreepool.com

How about impact of pH and Borates on needed FC levels? Other info sources I reviewed:

• 2.0 to 4.0 Free Chlorine May Not Work • Pool Chemistry Training Institute
• Optimizing SWG use: Higher CYA, Borate and Free-Chlorine Levels Needed • Pool Chemistry Training Institute

As I understand it:

• pH tends to run higher when using SWG (and when trying to manage my LSI with colder water in the winter in San Diego) - so then do I need higher levels of FC?
• Borates (50 ppm) should change min FC level needed from 7.5% of CYA level to 5% of CYA level - so then do I need lower levels of FC?

Thanks!

 

[Strategerizer]

I have an in-ground pool/spa combo where water circulates from spa to pool via spillway/waterfall. I am in Southern California (San Diego) and pool water gets 50 - 55 degrees measured in the coldest part of the pool first thing in the morning. I don't heat the pool in the cold season but may heat the spa (about once a week) to 102 degrees and that water circulates in the pool once done. IntelliFlo VS filter pump runs daily about 5 - 6 hours on low speed. (BTW, I am keeping water LSI balanced though a bit tricky during cold season because need to have it balanced across the whole range of 50 - 104 degrees!)

Not sure what best practice would be with the SWG... I have a Hayward AquaRite system that has minimum operating temp of 50 degrees. Just replaced the original T-15 cell with an aftermarket from CircuPool and I think their min operating temp is 60 - 65 degrees.

Should I turn off the AquaRite until water temp rises to 65 or 70 degrees and manually chlorinate? (That would be a hassle...)

Can I keep min chlorine levels lower during the cold season?

Maybe if I keep the SWG on and water is very cold and the cell does not produce chlorine, well probably algae/bacteria won't grow either... and then chlorination will kick in whenever I heat the hot tub, so maybe that is enough?

Thanks!

 

[woodyp]

I'm pretty sure adding borates or not shouldn't effect our recommended levels for FC with a SWCG. I ran berates one summer as a test without a SWG with zero effects. Onecofcour resident gurus will probably Chime in.

 

[JoyfulNoise]

I have a SWG pool and plan on adding Borates. SWG makes keeps my pH range on the high side. I know the TFP's recommended min and target levels of Chlorine at different CYA levels :

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.

www.troublefreepool.com

How about impact of pH and Borates on needed FC levels? Other info sources I reviewed:

• 2.0 to 4.0 Free Chlorine May Not Work • Pool Chemistry Training Institute
• Optimizing SWG use: Higher CYA, Borate and Free-Chlorine Levels Needed • Pool Chemistry Training Institute

As I understand it:

• pH tends to run higher when using SWG (and when trying to manage my LSI with colder water in the winter in San Diego) - so then do I need higher levels of FC?
• Borates (50 ppm) should change min FC level needed from 7.5% of CYA level to 5% of CYA level - so then do I need lower levels of FC?

Thanks!

So a little bit of history is in order - TFP doesn’t subscribe to Robert Lowry’s school of thought on pool care. He was a guy who worked in the pool chemical supply industry for most of his career then likes everyone to think he suddenly had an epiphany about pool chemistry. He likes to pretend that he came up with the FC/CYA ratio back in the 90’s but didn’t do anything about it and that Richard Falk (aka, chem geek) proved that he was right when Richard started publishing his thoughts about it. He then came up with his Pool Chemistry Training “University” as a way of selling a pool care technique to pool service techs in the industry and make his money from that. Even though 99% of what he “discovered” was freely available information on the Internet years before he ever started his business. So let’s just leave it at that - no need to quote any of his “ground breaking thoughts” on pool care

The variation in active chlorine with pH is weak once CYA is in the water so the FC/CYA ratio can be considered independent of pH. You apply the same percentage no matter of your pH is 7.0 or 8.2. Anyone that claims otherwise isn’t paying attention to the science.

Borates make no substantial difference on the FC/CYA ratio used. They are a mild algaestat at best.

If you use an SWG to chlorinate, the TFP recommended FC/CYA ratio is 5% as the absolute minimum value your pool should be at. If you manually chlorinate with bleach or stabilized chlorine products, then 7.5% works better.

All of this information is freely available in TFP’s advanced pool chemistry threads. Just look up anything written by chem geek and you’ll find out all you need to know.

 

[Cena_sea]

For first winter with pool I decided to not turn off swg. I guess I was nervous to have it off for a while but I see people on here turn it off regularly.

I adjusted swg down to as low as 5%. Rarely have I had to use chlorine this winter. I am leaving swg at 5% now so I can use up leftover chlorine from last year.

 

[Strategerizer]

@JoyfulNoise, thanks for the feedback and providing context to other sources of information. This is very helpful in trying to reconcile advice found in different places. I came to learn that Richard Falk is the trusted wise man so good to know he is the one using Chem Geek alias!

If I don't put you on the spot, would you share your assessment of Orenda as a source of information? For example, they recommend keeping CYA at 30-50 vs. TFP recommends CYA at 80.

Further on Orenda... I know they sell specific products and take with a grain of salt info that promotes using them, like enzymes and the SC-100 chelator they sell. Per my understanding their enzymes can help with big bather load or foliage crud in the pool but for more average conditions relying on only chlorine is more practical and economical. I just used their SC-1000 chelator now (about 2 months after replaster/refill) and it ended up depleting all my chlorine + 2 gallons for 3 days. I am adding another gallon tonight but am thinking maybe my water is clean enough so the chelator has nothing to bind to so just ravages the chlorine... Maybe it will help with scale on the tile heating in the sun or in the heated salt cell... My first line of defense remains keeping LSI in balance and doing the calculation for both normal/cold water AND for 104 degrees (for when I heat the spa) so can avoid corrosion and scale regardless. Not sure if this chelator justifies the investment to keep it going moving forward... do you have an opinion on this?