Intellicenter vs Test Kit Salt PPM

[LSU]

We just converted to salt water 2 days ago. I have been looking at Intellicenter giving me a salt ppm number from the probe that's with the IC60 I assume. That number doesn't jive with the test I just did this evening. My test with my salt pro test kit was 3400 ppm. We tested the water prior to adding any salt, and i realize that number is a bit high. The reading coming off the SWCG/Intellicenter was at 2850, and last night I believe it was reading a 2900. I'm going with the test kit numbers, but why is the reading from the SWCG so far off?

 

[Jimrahbe]

LSU,

The cell does not directly measure the salt level, it kind of guesses at it based on the conductivity of the water.. Its accuracy is +/- 500 ppm.

Your test kit is much more accurate.

That said, you can often replace the cell's flow switch and get lucky and get the cell to read closer, but it is not necessary..

I never trust what my cell reports unless it is near what my K-1766 reads.

The downside is that the cell will show low salt if it just 'thinks' the salt is low, no matter what the actual salt level is. So, in your case, once the reported value falls below 2800 it will start showing low salt.

Thanks,

Jim R.

 

[LSU]

The downside is that the cell will show low salt if it just 'thinks' the salt is low, no matter what the actual salt level is. So, in your case, once the reported value falls below 2800 it will start showing low salt.

Well that sucks, lol. Is there no way to calibrate that? I see what you are saying...basically it's already false and when it drops to what the reporting level would be doesn't necessarily mean it's really low, but it's going to stay in alarm anyway. Ugh...that messes with my OCD and it hasn't even happened yet

 

[LSU]

It looks like there was a way to reset the older model SWCGs, but I have a new one. I can't believe they have no way to reset it or something.

 

[JamesW]

No test is 100% accurate.

You have to know the accuracy, resolution and tolerance of each test and that gives you a range for the test.

For example, if the tolerance of each test is +/- 300 ppm to 99% certainty, then the 3,400 ppm is actually 3,100 to 3,700 ppm to 99% certainty.

The 2,850 ppm is 2,550 ppm to 3,150 ppm with 99% certainty.

So, you need to see if the ranges overlap.

If they do, then the actual number is likely to be in the overlap.

So, that could suggest that the actual number is between 3,100 ppm and 3,150 ppm.

If the numbers don’t overlap, then one or both tests are likely to be off for some reason.

You can also do more tests and get more ranges to see if you can find more overlap.

For example, if you got a salinity test meter, it might have a reading of 3,000 ppm +/- 200 ppm.

The biggest mistake people make is seeing a test result and thinking that it is exactly accurate.

The K-1766 measures chloride and it reports in units of sodium chloride.

It assumes that all chloride is from sodium chloride, but some comes from other sources of chloride like calcium chloride.

The SWG measures conductivity, which is affected by all ions like calcium, sodium, potassium, magnesium, chloride, bicarbonate, carbonate, cyanurate, sulfate etc. but it reports in units of sodium chloride.

So, you are measuring conductivity of all ions but reporting as if it were 100% from sodium chloride.

Even if a test says +/- 200 ppm, this assumes that the test is working perfectly under ideal conditions and being done exactly right.

It also assumes that 100% of the ions in the water are from sodium chloride.

This is rarely true.

Because the two tests are really testing two different things (Water conductivity vs. chloride level), they are not going to agree completely even if the tests were 100% accurate, which they are not.

In any case, your numbers are close enough.

If your OCD gets bad enough, get a conductivity meter and get some more data to see what that shows.

I never really trust any single salinity test.

I always want at least three that are in close agreement within the tolerance of each test.

 

[JamesW]

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[JamesW]

 

[JamesW]

Whenever you are measuring something, like temperature, salinity, pressure etc. you have to think in terms of probability, accuracy, resolution and tolerance.

If you get a reading, there is always a probability distribution that provides a range of results.

For example, a reading of 3,200 ppm from a meter might be +/- 100 ppm to within 1 standard deviation, which means that there is a 68.27% chance that the actual number is between 3,100 ppm and 3,300 ppm.

If you want 95.45% certainty. that might be +/- 200ppm.

99.73% certainty might be +/-300 ppm.

Even then, there is always the possibility of some sort of defect or malfunction that makes the test inaccurate.

Maybe the batteries are going bad or the meter needs to be cleaned or calibrated or the meter is malfunctioning or the temperature sensor is off etc.

And, there is always the possibility that there is some sort of defect in the process of doing the test or in getting a sample.

Maybe the sample bottle is contaminated.

Maybe the person uses the wrong sample size or the wrong multiplier.

Even if the sample size is off by a tiny bit, it can make the result inaccurate.

Maybe the person is not holding the dropper correctly etc.

Maybe the salt has been added but it is sitting on the floor and it is not mixed into the water.

Maybe there is rain water on top and the cell is getting the wrong reading.

 

[Newdude]

Due to this dilemma, I wait for the idiot light to come on. Then I test to confirm before adding salt. A few times this year the low salt light was due to big storms that took a while to mix.