SWG reading vs TDS digital meter

[stunatu72]

Hello. I decided to get a TDS meter to see how it compares vs SWG salt reading. The meter gave me TDS of 2000 ppm. My AquaRite SWG indicates salt at 2900 ppm. I’d assume TDS would return minimum 3200 ppm if you assume 2900 salt + 200 ppm calcium + 90 ppm of alkalinity + 30 ppm of CYA.

Every end of season I purge 44% of my pool volume of 65,000 L. The math says my salt concentration drops by 1272 ppm when the water is replaced by rain etc. The math also says to add 4 bags or 80kg of salt to get back to 2900 ppm for salt. I’ve been adding 4 bags for 14 years and it always lines up vs SWG reading.

Any thoughts on what to trust or what to ignore? Salt test strips in the past have indicated -800 pmm vs SWG but my Taylor chlorine tests always put pool FC and TC at 3-4 ppm. So I’ve always assumed SWG salt level reading was ”ok” or fairly close. I run the SWG at 15%-20% and pool is crystal clear, no algae, no problems.

 

[PoolStored]

I would get a Taylor K-1766 or TFTEstkits.net Salt test and trust it. Ignore the meters, strips and pool store testing.

 

[ajw22]

The Taylor K-1766 salt test is the gold standard.

A salt test meter can lose calibration over time and you would not know it.

Test strips are worthless.

A TDS meter tells you nothing actionable.

 

[stunatu72]

I would get a Taylor K-1766 or TFTEstkits.net Salt test and trust it. Ignore the meters, strips and pool store testing.

Thanks. That was the next step. That said, what if the test tells me the salt level is 500 or 600 ppm lower vs generator? By adding the salt to match needed level, would the SWG not trigger a high salt warning? Should I just ignore all this since my pool chlorine levels are perfectly fine and within needed range?

 

[stunatu72]

The Taylor K-1766 salt test is the gold standard.

A salt test meter can lose calibration over time and you would not know it.

Test strips are worthless.

A TDS meter tells you nothing actionable.

I thought the TDS reading would be an interesting input into the LSI calculation for the Orenda calculator.

 

[mknauss]

An Aquarite does not measure salt level. It measures efficiency of the cell. So you are using the salt test kit for when the SWCG is showing low salinity. The SWCG will show that as it ages. You do not want to add too much salt based on that.

We use CSI for calcite saturation.

 

[PoolStored]

I would get the test, then post results. We deal with it when we know your salt level.

In general, the cells typically report lower.

Ignore TDS and use Pool Math. Link-->PoolMath

You have a vinyl pool, you don't need to track LSI or CSI...

 

[ajw22]

Thanks. That was the next step. That said, what if the test tells me the salt level is 500 or 600 ppm lower vs generator? By adding the salt to match needed level, would the SWG not trigger a high salt warning? Should I just ignore all this since my pool chlorine levels are perfectly fine and within needed range?

 

[JamesW]

The meter gave me TDS of 2000 ppm.

My AquaRite SWG indicates salt at 2900 ppm.

2,000 ppm TDS corresponds to a salt of about 1,350 ppm.

2,900 ppm salt is 4,400 ppm TDS.

So, one, or both, of your readings are way off.

Get the K-1766 salt test kit.

If you get a meter, get a good one that reads salinity as sodium chloride.

What meter did you get?

A meter needs to be set to NaCl salt and never TDS.

TDS is not a valid reading for a salt pool.

TDS assumes that the water contains the following: 40% sodium sulfate, 40% sodium bicarbonate, and 20% sodium chloride.

442™: Your PoolMeter™ has been factory calibrated with the TDS 442 Standard Solution. The 442 Standard Solutions consist of the following salt ratios: 40% sodium sulfate, 40% sodium bicarbonate, and 20% sodium chloride. This salt ratio has conductivity characteristics closely matching natural waters and was developed by the Myron L® Company over five decades ago.

 

[proavia]

Use the PoolMath app instead of the Orenda one.
PoolMath calculates CSI instead of LSI.
CSI is a better indicator for pools instead of the old LSI, which is used for boilers.

 

[ajw22]

Read CSI and LSI - Further Reading

 

[stunatu72]

An Aquarite does not measure salt level. It measures efficiency of the cell. So you are using the salt test kit for when the SWCG is showing low salinity. The SWCG will show that as it ages. You do not want to add too much salt based on that.

We use CSI for calcite saturation.

Thank you. This gives me better perspective. I knew that CH had to be maintained for Pentair heater warranty but was monitoring as I noticed some scaling on liner. Learned about CSI today so switching to that. Thanks.

 

[stunatu72]

Use the PoolMath app instead of the Orenda one.
PoolMath calculates CSI instead of LSI.
CSI is a better indicator for pools instead of the old LSI, which is used for boilers.

Will do. Thanks!

 

[stunatu72]

This is great info. Thanks!

 

[stunatu72]

I would get the test, then post results. We deal with it when we know your salt level.

In general, the cells typically report lower.

Ignore TDS and use Pool Math. Link-->PoolMath

You have a vinyl pool, you don't need to track LSI or CSI...

Thanks. Test kit ordered but delayed by a week. I’ll post my results end of next week.

 

[stunatu72]

I would get the test, then post results. We deal with it when we know your salt level.

In general, the cells typically report lower.

Ignore TDS and use Pool Math. Link-->PoolMath

You have a vinyl pool, you don't need to track LSI or CSI...

So I received the K-1766 salt kit (they sent me 2 sets of reagents, one expiring/expired this year and one expiring next year) so tested salt twice. I got 2700 ppm of salt (exp 2024) and 2800 ppm (exp 2025). My SWG indicates 2800 ppm so spot on. I’ve got it running at 15%.

So with a CSI of 0.15, I was thinking of leaving the water alone. Unless folks think I should bring pH down to 7.6 - 7.8. Thoughts?

 

[ajw22]

Lower your pH a bit as it will only keep rising.

Keep your pH between 7.6 and 8.0

 

[stunatu72]

Lower your pH a bit as it will only keep rising.

Keep your pH between 7.6 and 8.0

At a pH 7.6 l, CSI would be -0.24. That would be considered much better vs 0.15 for a vinyl salt pool?

 

[PoolStored]

CSI doesn't matter for a vinyl pool. If you are tracking in pool math, turn it off...

 

[JamesW]

High CSI can cause scaling in vinyl liner pools and in the SWG.

Keep the pH down some until the TA reduces to about 60 to 80.