Difference in PPM, which one is correct?

[cjryan33]

I have a 26,000 gallon in-ground salt water pool. The pool is about a year old. The Hayward Goldline controller is reading my salt levels at 2600ppm. I had my water tested yesterday and everything looked good except there is a big difference in the ppm levels. My water test shows that my pool is at 3100ppm. Which one is correct? I was about to add some salt to the pool before the test and now I am not sure.


Since it was time to do so, I cleaned my SWG and pulled my DE Filter out and cleaned that as well. After cleaning everything my pool is still reading 2600 ppm. Is there anyway to reset the controller and have it take a new salt level reading? Any assistance would be appreciated.

Thanks,
Chris

[mas985]

What really matters is what the unit is telling you because if it doesn't think the salt level is correct, it will shut down. So adjust the levels to keep the unit happy and produce chlorine.

However, cells will tend to read low when they are nearing end of life so the difference between what the unit reads and actual salt measurements are important but the other tests need to be reliable and pool store tests are not always reliable.

Also, I found the Goldline salt readout to be fairly accurate and nearly always will match my Taylor salt drop kit within +- 100 ppm. However, I have had problems with salt strips in the past and they tend to read high plus they can easily go bad if not stored properly so I no longer use those. Also, if the pool store used a TDS meter, those need to be calibrated to read accurately. So unles the pool store used a drop, I wouldn't trust the results.

[PoolDoc]

I'm probably not going to make your day, by telling you that they may both be 'right'!

For all salt test methods used by pool owners -- who don't have access to an analytical lab -- the difference between 2600 ppm and 3100 ppm is within the error range of the test methods. In other words, your likely actual salt level is probably somewhere between 2400 and 3300! If you are using test strips, than the error range on those is more like 2000 - 4000 ppm!

If you want to know your salt level more accurately, or if you want to calibrate your SWCG, the most accurate readily available kit is the Taylor K-1766. You can order it from Amata via Amazon: Taylor K-1766 (http://www.amazon.com/Taylor-Salt-Water-Test-K-1766/dp/B001DO35EU/ref=as_li_tf_tl?ie=UTF8&tag=poolbooks).

Accuracy on those kits is rated as better than 1 drop (200ppm) + 10%. This means your error around 3,000 ppm would be ± 500 ppm (300 + 200), but it would probably do better than that. It's not a bad idea to get that kit -- the sensors on SWCGs can 'drift' and recalibration assures you that your SWCG is not 'beating its head against a wall' by trying to generate chlorine when there's not enough salt in the pool.

[ Mark and I were posting at the same time. I'm surprised that the field accuracy of the Taylor unit is that good -- but they do try to be careful in their accuracy ratings. The K-1766 is the ikt he's talking about. Also, if it sounds like we're contradicting each other, we're really not, so re-read our posts. ]

[cjryan33]

Thanks for the information. I have ordered the Taylor K-1766 salt water test kit. I would hope that my salt cell is not going bad since it is just over a year old. Once the kit comes in and lets say I test the water and it says the the pool is at 3000ppm. From what I read above, I should be able to go into the controller and calibrate it and change it to display 3000ppm?

[PoolDoc]

I wouldn't worry, simply because of a variation in test results.

As far as calibration -- some can be. Look up your exact model manual here,
http://www.hayward-pool.com/ctg/In-Ground-Pool-Sanitization-Salt-Chlorination_10201_10551_-1_27501_14006_Y.htm
and see.

[steveinaz]

I have the Taylor kit Ben mentioned---soooo much eaiser than the strips, with accurate, repeatable results.

[mas985]

As far as calibration -- some can be. Look up your exact model manual here.
The Goldlines cannot really be calibrated for salt level. The best you can do is replace the average salt level (shown in main display) with the instaneous salt level (shown in the SWG diagnostics menu) which explained in the manual.

[BigTallGuy]

For what its worth, My SWCG (Compu-pool CPSC24) shows my "ADD SALT" light when the weather is cold almost all the time. I don't get an exact reading just an idiot light. SWCG's measure the Salt level electronically and water temperature plays a big part in that reading. Once your pool water goes below 60° F most SWCG's stop producing chlorine or produce greatly reduced amounts of chlorine.

Where are you located and what is your water temp? Unless you are heating your pool, you might want to wait until the water warms up before adding salt. And as mas985 already mentioned, the SWCG is what has to be satisfied to work properly.

[cjryan33]

I live in Fulshear, TX just oustide of Houston. If I recall correctly my water temperature is about 73°. I am going to wait to add any salt until after I test it when the kit comes in. The store test that I did last Saturday just kind of surprised me because the PPM levels have usally been within 1-200 ppm. Thanks for all the information.

[waterbear]

I would like to point out a few things:

1. a difference of 800 ppm between the readout on a Goldline unit and a chemical test for choride ion can be off by as much as 800 ppm and still be 'in spec' according to them.

2. chemical tests (both drop and strip) measure chloride ions, readouts and handheld meters measure conductivity and approximate the salt level (but make some assumptions about the actual ionic makeup of your water to do so). Comparing conductivity to chloride ion concentration, while it can be close is really comparing apples and oranges!

3. Since the salt cell is measuring conductivity and not chloride ions that is probably better, as MAS985 pointed out, to go by what the cell is saying the salt is rather than an outside test, be it chemical or conductivity since if the cell THInKS the salt is too high or too low it will shut down and if the actual salt is somewhere in the ballpark (say 1000 ppm) then you should be good to go!

4. conductivity is affected by water temperature, even with so called 'temperature compensated' meters (once again making assumptions about the water makeup to convert conductivity into salt). Measure at NORMAL POOL TEMPERATURE! Cold water will always show low salt because conductivity drops when temperature drops.

5. silver nitrate/chromate titration tests for salt, while having the greatest precision, are very easy to overshoot on endpoint and are a test where the usual titration advice of "add one more drop until there is no more change in color" is NOT applicable! Strips are also based on silver's reaction with chloride but their precision depends on the actual concentration of chloride present and precision tends to go down as salt levels rise but are much easier to get an accurate endpoint (but the need for precision also becomes less as the salt level rises in actual practice so strips are often more than adequate!). The main problem with strips is not letting them sit in the sample long enough. Aquacheck recommends 10 minutes. I know the LaMotte strips are fast strips but know nothing of their chemistry and have heard that they are more difficult to use than the slower AquaChek, which are actually chloride capillary titrators.

6. As far as pool store meters and handhelds , there are good ones and bad ones. MyronL makes a good one as does Eutech/Oakton (resold as a Goldline salt tester). Hanna Instrumetns meters (also resold under the LaMotte brand) not so good IMHO.*

+ ANY meter needs to be calibrated against a standard solution on a regular basis (weekly is standard practice) but since the standard solutions can be expensive many overlook this so the readings the meters give are worse than useless!

7. (and the most important point) As MAS985 pointed out, the salt level that your cell THINKS is present is what is really important and if other tests show that you are in the ballpark (within 800-1000 ppm) AT NORMAL POOL TEMPERATURE) then don't lose any sleep over it and ENJOY THE POOL!

+ IF your cell says that the salt is very low while a chemical test or handheld meter says it's very high then you either have a cell that needs a good acid cleaning to remove the scale or one that is dying and needs to be replaced.
+ IF you have a cell that reads very high salt while chemical tests indicate low salt you have a bad cell or control board in your unit.

[PoolDoc]

The main problem with strips is not letting them sit in the sample long enough. Aquacheck recommends 10 minutes. I know the LaMotte strips are fast strips but know nothing of their chemistry and have heard that they are more difficult to use than the slower AquaChek, which are actually chloride capillary titrators.


Does AquaCheck still recommend this? All I could find on their not-very-informative website last night was a mention of 4 - 5 minutes.

[waterbear]

Does AquaCheck still recommend this? All I could find on their not-very-informative website last night was a mention of 4 - 5 minutes.

http://www.aquachek.com/newspdfs/ProductMemoSalt_rev3.pdf

[PoolDoc]

Ok, I've archived that. Do those instructions still apply to all current test strips?

Here's a copy, with my emphasis added:
A recent change in our manufacturing process may cause the gold/yellow completion band on top of strip not to turn dark to indicate that the test is complete as stated on product instructions. The intended chemical reaction still occurs and an accurate test result will register in no more than 10 minutes. The test reading will be accurate regardless of status of the gold/yellow band on top of strip.


================================================== =======================
From AquaCheck newsletter, linked above:

Please be assured our test strips continue to be made under the highest quality controls and we apologize for the inconvenience.

Current instructions on both products read:


1. Fill a small vial with about one inch of pool/spa water.
2. Remove one strip from bottle and replace cap immediately.
3. Insert lower end of strip into water. Do NOT immerse yellow completion band at top of strip. Important: Keep top half of strip completely dry to get an accurate reading.
4. Leave strip in water unless test is complete (when yellow band turns dark, about 3-*-4 minutes.)
5. Obtain your salt concentration: note where top (highest point) of white peak falls on the number scale. Read top of peak to nearest 0.2 division. Locate the sodium chloride concentration next to that reading in table below.

Instruction changed for Lot # from 9349 to 0236:

1. Fill a small vial with about one inch of pool/spa water.
2. Remove one strip from bottle and replace cap immediately.
3. Insert lower end of strip into water. Do NOT immerse yellow completion band at top of strip.
Important: Keep top half of strip completely dry to get an accurate reading.
4. *Leave strip in water for 10 minutes and compare strip to chart for results.
5. Obtain your salt concentration: note where top (highest point) of white peak falls on the number scale. Read top of peak to nearest 0.2 division. Locate the sodium chloride concentration next to that reading in table below.
================================================== =======================

[waterbear]

Ok, I've archived that. Do those instructions still apply to all current test strips?



Don't know but 5 discovered on my own thatn 5 minutes ofent ws not long enough for the liquid to travel to the top of the strip and turn the top dark with the older strips but when I gave it a full 10 minutes the srip would be on the money (at least pretty close in the ballpark) with a calibrated goldline (oakton) salt meter

[PoolDoc]

Don't know but 5 discovered on my own thatn 5 minutes ofent ws not long

Didja spill some bleach on your keyboard?? ;) ;)

[waterbear]

Using the notebook and just not used to the small keyboard! That's what I get for perusing the board by the pool instead of soaking in the hot tub with a beverage!

[PoolDoc]

Yeah, I've got to get a iPad soon. About 15% of my users, are using one, and the percentage is climbing fast.

(Susan doesn't usually get excited about new tech -- she just sees $'s going down the drain -- but she'll get the iPad come fall, and she can think of a number of ways that one could help her as she moves among classrooms.)

[cjryan33]

So the Taylor Salt Water test kit came in and I was able to test the water last night. The Goldline system is reading 2700ppm and the test kit stated that I was at 2800ppm. It appears that my system is closer to the actual levels than the pool store. The said my levels were at 3100ppm. This makes me feel better.

[PoolDoc]

I'm glad it worked out for you . . . and a little surprised that the results are so close together. That does suggest that your actual salt level is somewhere between 2650 and 2850 ppm -- it may not seem like it, but that's a really high accuracy reading!

[waterbear]

Also realize taht the goldine precision is as high as 800 ppm so both your reading AND the pool store reading are in spec!