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Thread: Salt Level Testing

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    texasbrew's Avatar
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    Salt Level Testing

    I am trying to figure out if I have an issue with my salt sensor. My Jandy Aquapure is reading the salinity to be 2700 whereas the Aquacheck test strips indicate that my salt is around 3800. I cleaned the cell yesterday with the diluted MA and I did not see any fizzing that would indicate a calcium buildup. I am reluctant to use the local pool stores as their results seem to vary from the TF-100's results for items such as TA and PH. The Jandy website indicates that there may be a margin of error on test strips of up to 800. A margin of error of 800 could also mean that the salt level is actually 4400. At this point I am not certain if I should add salt or get water tested at a couple of pool stores and see if their reading is close to either the sensor or the test strips and assume that one or the other is correct. I believe that optimum for the salt cell on the Jandy is 3000 to 3500.
    PG-500, WSM, 20K Gal gun pool w/ Aqua Pure 1400 SWG, flagstone coping, gray plaster, DE Filter, 400K BTU nat gas heater and Polaris 280 cleaner

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    duraleigh's Avatar
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    texasbrew,

    To this point, the Aquacheck strips have been right on the money. Naturally, I would defend them but, from what I've heard about them, they're one of the few strips that are pretty darn consistant. I think what you'll have to do is get at least one more "opinion" by having a different test done by someone else.

    Please let me know if the Aquacheck strips are very far off the mark......your's will be the first reported but it's important that I know. Thanks!
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    JasonLion's Avatar
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    I would trust the test strips. Many of the SWGs show a lower than actual salt reading when the water is cold.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    texasbrew's Avatar
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    At what temperature could I expect the strips and SGW readings to converge? I believe that my water temp at last check was 70 deg F.
    PG-500, WSM, 20K Gal gun pool w/ Aqua Pure 1400 SWG, flagstone coping, gray plaster, DE Filter, 400K BTU nat gas heater and Polaris 280 cleaner

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    JasonLion's Avatar
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    Normally salt sensors are most accurate when the water is between 80 and 90 degrees. The AquaPure appears to be temperature compensated. Even temperature compensated salt sensors can be off a bit when the temperature is very low, but not generally as far off as you report.

    have you tried cleaning and running the auto re-calibrate on the salt sensor? From the AquaPure manual:

    One time per year or as needed. It is rare but scale formations on the Flow/Temp/Salinity Sensor sometimes
    occur and will affect the accuracy of the salinity test.
    1. Remove Flow/Temp/Salinity Sensor from the threaded PVC Tee or 3-Port Cell by turning
    counterclockwise or removing the union nut.
    2. Brush with a mildly abrasive green fi ber household cleaning pad. Contacts should be clean and bright.
    3. Thoroughly rinse the Flow/Temp/Salinity Sensor with clean tap water. Replace and resume normal
    operation.
    4. Turn power off and back on in order to recalibrate and reset Flow/Temp/Salinity Sensor. Reset
    anytime Flow/Temp/Salinity Sensor is unplugged.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    I always have my salt checked when at the pool store and that test is always consistent so I believe they are doing it correctly. They use a small meter type device that has a small bowl. I always get 2100ppm and that is roughly were I started at, I do not have a SWG, just add salt for feel.

    I have seen pool store mess up different tests from same sample but salt has always been the same.
    20x40 24,000 gal IG plaster/CircuPool RJ45 SWG/2 skimmer/2sp 2.5hp Jandy Stealth/340sq ft cart filter/600sqftHeliocol Solar Panels/6ft semi circlr tanning ledge/25ft deep end bench/5ft sheer descent/2 lion head water features/1300sqft travertine paver/2 Colorlogic lights/Hayward Navigator/3step 2ft raised bond beam

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    Inconsistent salt readings w/Aqua Rite - same problem?

    My new Aqua Rite sysetm (w/T-15 cell and new flow sensor) shows salt
    at 2,600 ppm whereas the AquaCheck strips reads 6.2 or 4,270 ppm
    (several times).

    Took water sample to pool store & their strip reading was in the same
    neighborhood. Thought I might have bad bottle of strips. Apparently not.

    Is cold water (62 degrees) an issue with Aqua Rite systems as well? Pool
    is 8 years old and I don't recall this probelm in the past.

    Any other reasonably inexpensive way to confirm actual salt reading? Don't
    want to dump in more salt if 4K reading is correct...

    Thanks!
    20K, Salt Water, Gunitte, Aqua Rite chlorinator

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    texasbrew's Avatar
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    I made it to the pool store on Sunday and their test came back at 3200 PPM (slightly higher than the cell is currently reading - 2800 PPM). I asked the tester and he said that they were using a drops based test. I am not sure which value is correct at this point.

    Thanks
    PG-500, WSM, 20K Gal gun pool w/ Aqua Pure 1400 SWG, flagstone coping, gray plaster, DE Filter, 400K BTU nat gas heater and Polaris 280 cleaner

  9. Back To Top    #9
    Guest
    drop based kit has an accuracy of 200 ppm usually so their 3200, IF they did the test correctly, is pretty close to what the strips read. The strips have a variable accuracty depending on the ppm level you are reading but it is generally in the 200-400 ppm area for the normal range of salt we are testing for. So, if the drop test was reading low by 200 ppm and the strip high by 400 ppm then your results are right on the money! (and they are in spec for the accuracy of the SWG)
    remember, its a pool, not rocket science!

    As far as water temp goes, just about every SWG on the market (goldline included) will read low salt when the water is cold. This is not really a problem since cold water lowers the conductivity and to the cell this looks just the same as a low salt conditon. The only difference is that the conduvity will go up as the temp does.
    In other words, don't loose a whole lot of sleep over it. The strips are going to be "close enough for government work"!

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    I have the Aqualogic chlorinator which is very similar to the Aquarite unit and actually uses the same cell. Mine is about 3 years old so it may work slightly different than yours. After much research and testing on my unit here is what I have found.

    First, I confirmed with a Goldline tech that the Aqualogic unit does compensate the salt reading for temperature and I would assume that the Aquarite units also compenstate for temperature although I am not sure about one that is 8 years old. To confirm this myself, I ran my spa from 55 degrees F to over 100 degrees F with the same salt level and found the salt reading not to change by more than one step (i.e. 100 ppm). This would not be possible if the unit did not compenstate the salt reading for temperature. Given that the salt reading is fairly constant over temperature, I would assume that the temperature compensation is sufficient.

    I have noticed that when subjected to a very fast change in temperature, the unit will not adjust fast enough to compensate. I only see this problem when I first turn the solar on and I see that the current spikes but the temperature sensor is a bit slower in reading the change in temp so I suspect that is the reason. Once stabilized, the reading returns to the correct value.

    Also, I believe that most SWGs do compensate the salt reading but not all compensate the chlorine output for temperature. The pool pilot has long had chlorine output temperature compensation and the current generation Aqualogics have it as well but historically, most units did not do this.

    Without temperature compensation in the salt reading, the error would be signifcation at temperatures far from the calibration point. For example, assuming the SWG did not compensate for temperature and the manufactures calibrated at 82 degrees F, then the error at 55 degrees would be close to -900 ppm. At 70 degrees the error would be -500 ppm. At 95 degrees the error would be about 400 ppm.

    I also confirmed with the tech that they actually use the current sensor reading to trigger high and low salt readings and not the actual salt display. They primary reason is that their concern was to protect the unit circuits against too much current draw at the high end and too little chlorine production at the low end.

    Now this is not to say that there is no error in the SWG salt reading. I have found that my SWG also reads consistently lower than the strips. I believe this is a calibration issue with the SWG although I have yet to confirm this with the Goldline techs.

    The SWG measures the salt level by very similar method used in TDS measurements. Using the amps and voltage reading to determine the conductivity of the water, the unit then uses a formula which converts conductivity and water temperature into salinity. Because the conductivity of the water is dependent on not only the NACL in the water but other solids, the SWG would normally read higher than the actual NACL level. My unconfirmed belief is that Goldline calibrates the SWG to read lower than normal because they cannot compensate for other solids in the water. Probably to ensure the owner puts enough salt in the water. I am not sure they would confirm this even if it were true.

    Here is another good source for conductivity.
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater, ThePoolCleaner

  11. Back To Top    #11
    Guest
    whether the goldline unit you have is temperature compensated or not depends on the software revision of your main board. The very newest ones are but I don't believe that any of the units that are over 2 years old are. My aqualogic is not temperature compensated and I do see the type of errors in salt reading that are described in the post above.

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    mas985's Avatar
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    Quote Originally Posted by waterbear
    whether the goldline unit you have is temperature compensated or not depends on the software revision of your main board. The very newest ones are but I don't believe that any of the units that are over 2 years old are. My aqualogic is not temperature compensated and I do see the type of errors in salt reading that are described in the post above.
    I purchased mine in the summer of 2005 or a bit over 2 1/2 years ago. So I know that units that are at least that old do compensation. However, my primary point was that you can expect a lot of error if they don't do compensation.
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater, ThePoolCleaner

  13. Back To Top    #13
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    My PS-8 unit is 3 years old and does not do the temp compensation and I do see the type of errors that you describe. (This is about the time frame that they were upgrading the firmware with this feature. Unfortunately the only way to get the new firmware easily is to upgrade the main board!) Not a big problem for me since I live in Florida and keep my pool heated most of the year so my water temp stays fairly constant.
    As far as conductivity (TDS and salinity) meters go, they use a compensation factor to account for the different ionic species in the water. I don't know what Goldline uses in their SWGs but I know in their handheld salt meter ( a rebranded Eutech) the correction factor is .5 according to the manual (although the two that I am personally familiar with had come from the factory set to .55) This correction factor is making some assumptions about the ionic content of the water (it is set to a higher number to give a TDS reading) but it's considered 'close enough for government work'.

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    I have an AquaPlus unit, and I have noticed and documented that the salt reading will also vary with the pH. I typically get 100 to 200 ppm change with a pH change from 7.2 to 7.6.
    7,500 gal, IG pool, L shape 22' x 15', 1.5 hp pump, cartridge filter, AquaPlus SWG/Controller, Pebble-Tec liner.

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    texasbrew's Avatar
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    Just a followup...

    My AquaPure is now reading 2900. I have not done anything since I last posted but cleaned out the de filter and replaced a bunch of lost water due to cleaning out of the de filter. I have not added any salt. Therefore, it seems that my water's temp (now 80 deg F) was a big reason for the salt reading low on my unit compared to the salt strips.


    Thanks.
    PG-500, WSM, 20K Gal gun pool w/ Aqua Pure 1400 SWG, flagstone coping, gray plaster, DE Filter, 400K BTU nat gas heater and Polaris 280 cleaner

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