SI is not just about scaling

[archonis]

" he had a digatal salt meter that showed the salt level to be 3400ppm, my test showed 3600ppm, the ic40 showed 2300ppm."
With my math above will show this being correct
" Btw the water was 64 deg" - will make the cell read lower then norm.


"all summer (78 / 87) the ic40 has read from 500 to 1000ppm less than the Taylor test. There were a couple days when it was nearly correct but then the next day it went back to +-1000ppm low."

the cell it self will have a 200 to 500 ppm deff. Your taylor will not even be correct. That why you are seeing so many readings that are not the same.
If you take your pool water to three stores on the same day not one reading will be the same when it comes to salt. it will always have a + or - 500ppm.

some days it was almost correct? tell me its right. nothing wrong. What if your SI? When was it last checked?

 

[JasonLion]

Re: ic40 salt level calibration

3,061ppm is not even counting your SI or what I call bad salt so your cell could be showing low salt.

SI really doesn't have much anything to do with this. The SWG is measuring conductivity. Conductivity varies with a number of factors, but in nearly all pools the only ones we actually need to worry about are the salt level and the water temperature. The only time SI would really matter is when SI is too high and you are getting calcium scaling on the salt sensor probe, which could cause wildly incorrect salt readings. From what bobby1017 has said, that shouldn't be an issue here.

The Taylor salt test is +-400 in the range we are interested in. The IC-40 is about the same. That does mean that we shouldn't expect the readings to match up exactly, but they also shouldn't be off consistently by more than about 800, and even that much disagreement is unlikely. Unless something fairly unusual is going on, a difference of 1,000 or more indicates bad calibration.

All that said, even bad calibration rarely matters. As long as the SWG continues to produce chlorine, it doesn't make any difference what it thinks the salt level is or how far off that is from reality. The only problem comes up when it is so far off that it shuts down and refuses to produce chlorine when the salt level (and everything else) is normal.

 

[archonis]

Re: ic40 salt level calibration

If the SI is off then would it not pull the wrong voltage off the blades of the cell? The cell acts as a load! They use that load based on the water temp to get the salt readings.

The range for AK, CYA etc are so wide you can still be in range and your SI will be way off. SI tells you if your water is balanced. When salt cells are calibrated in the factory they are calibrated to balance water around 77F.

Ever here the story that a pool lost 1200ppm of salt in 24 hours. We all know you cant lose salt but the water temp changed among other chemicals. When this happens it changes your SI.

Every time I deal with a salt cell i look at the SI, that is truly your total water makeup that is passing through the cell. This plays a role on the voltage load and can have huge impact on the reading.

Most salt cells takes a reading about every 12 hours. This is another common problem when a user has the cell wired hot all the time. Your reading could be 3 days old or more.

"SI really doesn't have much anything to do with this. The SWG is measuring conductivity. Conductivity varies with a number of factors, but in nearly all pools the only ones we actually need to worry about are the salt level and the water temperature. The only time SI would really matter is when SI is too high and you are getting calcium scaling on the salt sensor probe, which could cause wildly incorrect salt readings. From what bobby1017 has said, that shouldn't be an issue here"

SI has a lot to do with it. We also know that high SI creates scaling. Would that not change the load? SWG do measure the conductivity but thats based on the load.

Set up s 500gal tanks and start changing the make up. You will notice a lot when you start doing your bench testing.

 

[JasonLion]

Re: ic40 salt level calibration

If the SI is off then would it not pull the wrong voltage off the blades of the cell? The cell acts as a load! They use that load based on the water temp to get the salt readings.

SI is a measure of calcium saturation, which can be calculated by plugging several other numbers into a formula. The voltage/current running through the cell depends on conductivity, which can also be determined by plugging several other numbers into a formula. Several of the standard readings, for example the salt level and water temperature, are used un both formulas. But otherwise, conductivity and SI don't really have anything really to do with each other. It is possible to prepare water samples with any combination of high/low SI and high/low conductivity.

The range for AK, CYA etc are so wide you can still be in range and your SI will be way off.

That depends on who's recommended ranges you are using. Our recommended ranges are tight enough that if you follow our guidelines you are almost never going to have any issues with SI.

SI tells you if your water is balanced.

Well, yes and no. "Balanced" is a fairly vague word in this context. SI tells you if your calcium saturation is balanced, i.e. calcium is neither dissolved out of the plaster walls nor is calcium scale deposited on the walls when SI is near zero. Calcium saturation is only one of a number of factors that enter into having "balanced" water in a more general sense.

When salt cells are calibrated in the factory they are calibrated to balance water around 77F.

Again, yes and no. Several of the modern SWGs are temperature compensated, so that they automatically correct for water temperatures anywhere from around 65 to 100. On the other hand, some SWGs are adjusted so they work ideally around 77, or really more like 70 to 85.

Ever here the story that a pool lost 1200ppm of salt in 24 hours. We all know you cant lose salt but the water temp changed among other chemicals. When this happens it changes your SI.

Salt levels can change very quickly in some unusual situations, mostly when you have an autofill system and a significant leak. When things like that are happening you have much worse problems to deal with than SI.

Every time I deal with a salt cell i look at the SI, that is truly your total water makeup that is passing through the cell. This plays a role on the voltage load and can have huge impact on the reading.

As described above this is only sort of indirectly true. SI is not one of the factors that determines to load the cell sees, though in some situations SI and the load the cell sees can both be changing.

Most salt cells takes a reading about every 12 hours. This is another common problem when a user has the cell wired hot all the time. Your reading could be 3 days old or more.

Again, kind of true but not really. A majority of the SWGs on the market average the salt reading over the last 24 hours. They take readings anywhere from continuously to once a minute, so long as the cell is on, and average those with all the other readings they took over the last 24 hours and show you the average. In most cases this gives a fairly good number. But there are situations, like right after you add a lot of salt to the pool, where the reading can be way off because it mostly shows what the level was in the 24 hours before you added the salt.

SI has a lot to do with it. We also know that high SI creates scaling. Would that not change the load? SWG do measure the conductivity but thats based on the load.

Under normal conditions the conductivity of the water directly determines the load on the SWG. SI does not directly enter into that. Scaling is a separate issue. If SI is significantly too high you will getting scaling inside the cell. The SWG cell plates become coated with calcium, which is an insulator, and that prevents the cell from working correctly. Depending on the brand of SWG you have that may or may not affect the salt reading on the display. However, this is a fairly unusual situation if you are following our recommendations. For most pool owners there is never any need to think about SI. Overall, only people who are for some reason unable to keep TA and/or CH levels in the recommended range need to think about it.

Set up s 500gal tanks and start changing the make up. You will notice a lot when you start doing your bench testing.

Indeed. However, it is also useful to take knowledge gained in that way and match it up with a knowledge of the chemistry involved to double check that you are assigning cause and effect correctly. For example, adding salt causes SI to go down and conductivity to go up and that can give you the impression that SI and conductivity are correlated. But PH changes can have a much more dramatic effect on SI, yet have very little impact on conductivity. Sometimes the two are related, and sometimes they are not. It is much simpler to look at the factors individually, i.e. salt, CYA, temperature, etc, instead of trying to draw parallels between two fairly complex factors that are only indirectly linked.

 

[archonis]

Re: ic40 salt level calibration

SI is not just about scaling. It was started years ago by water treatment plants as a way for water to be safe and balance. From a electrical stand point any changes you make to the water as a whole will change the way it treats the voltage. that is what the cell uses. goes back to ohms law. SI is a way to look at the water as a whole. That is what it is.

Any time you run bench test you always want to treat everything individuality. Change one factor and correct the others but we all one when dealing with chemicals one will counter act with another.

Salt cells are very chemical dependent. Most users do not understand that.

When dealing with salt cells there are a lot of factors you have to take in play.

Age - over time the blades and coating will break down and effect the readings
Temp Sensor - They will fell just like anything else (do math in earlier post to check that or wand it)
Operations - The overall health of the cell, LED's etc.

Those are just to name a few.

The bottom line is; 99% of all cell problems are chemical issues. 99% of the time the SI is out of range.

I however do not agree with everything in the above post. The 16K chip cant hold all of that info and that why they have bad feedback.

If anything comes out of this post i hope its that SI is not just about scaling. Its your total balance, Yes, Balance for scaling in stuff but at a electrical stand point it has a huge effect.

 

[JasonLion]

Having ranges for each level is very important, and covers many many issues that SI doesn't even begin to address. SI was developed by the steam boiler community to help deal with cast iron steam boilers at high temperatures and pressures. It was never intended to apply generally and has only tangential relevance to swimming pools. For swimming pools, it does not tell you anything useful beyond a general check on calcium pitting/scaling risks.

There is a tremendous amount of mis-information about SI in the pool industry. Many people have taken recommendations from the boiler industry and mis-understood and mis-applied them in a wide variety of ways. It is quite easy for SI to be balanced while the pool as a whole has wildly inappropriate levels.

I agree that maintaining appropriate levels is important, and way too often overlooked. We recommend specific ranges for each chemical to address this. Following our recommended levels takes care of everything most people should ever need to know. Adding in SI serves mainly to make things more complex and distract people from what is actually important. As mentioned previously, it can be very handy in situations where you have no choice but to allow very high CH levels. Otherwise it can be ignored.

 

[chem geek]

Re: ic40 salt level calibration

SI is not just about scaling. It was started years ago by water treatment plants as a way for water to be safe and balance. From a electrical stand point any changes you make to the water as a whole will change the way it treats the voltage. that is what the cell uses. goes back to ohms law. SI is a way to look at the water as a whole. That is what it is.
:
If anything comes out of this post i hope its that SI is not just about scaling. Its your total balance, Yes, Balance for scaling in stuff but at a electrical stand point it has a huge effect.

I'm sorry, but you are wrong about this. Though the saturation index was originally developed by Langelier for determining scaling potential in boilers (see this link), it is nothing more than a saturation measurement for calcium carbonate. It is not a measurement of the conductivity of the water which is related to TDS (though actual conductivity depends on the composition of TDS, specifically the types of ions and their charges). Though Ohms Law relates current and voltage to resistance, and though resistance and conductivity are inversely related, this has nothing to do with the saturation index which is ONLY about saturation of calcium carbonate.

You can see a detailed derivation of the calcite saturation index near the bottom of this spreadsheet (around lines 444 through 489) and also in this post where you can see that the formula comes directly from the solubility product of calcium ions and carbonate ions.

Now it is true that as the saturation index gets higher the risk for scaling at the cathode (hydrogen gas generation plate) is higher, but whether scaling actually occurs is dependent on other factors including the pH buffering in the water which is why having 50 ppm Borates helps to reduce scaling. Also, most modern salt cells reverse polarity to slough off any scale that may develop. Of course, this can only help to some degree and if the saturation index is too high then the scale can build up over time.

One can have very high conductivity (high sodium chloride salt level, for example) with a very low saturation index (very low calcium level, for example) and vice versa. They are not related to each other except that a high TDS or salt level slightly lowers the saturation index.

Why do you think that the saturation index has anything to do with the conductivity of the water? Where are you getting this kind of information?