Re: ic40 salt level calibration
archonis said:
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.
archonis said:
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.
archonis said:
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.
archonis said:
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.
archonis said:
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.
archonis said:
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.
archonis said:
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.
archonis said:
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.
archonis said:
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.