Difference in PPM, which one is correct?

[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/Pro...oSalt_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??