Salt Test Strip Question

[mickey4paws]

When we first installed our Aqua Rite SWG, the salt level on the panel was around 3100-3200 and an Aqua Check salt strip test was 3380. During the past few weeks, we had a sand filter that was leaking approximately 10 gallons a day. The Aqua Rite reads 2800 to 2900 (when it's generating and when I push the diagnostics button to get salinity), and I did a salt strip test last night and it read 3380. Also, I had to go to the pool store yesterday for something else so I had them test my salt level. They came back with 2600 but I don't trust their equipment at all.

My question is during the salt strip test, if you leave the salt strip in the water too long, does the salt value continue to climb? I have a hard time telling when the bar at the top of the strip turns dark. I had the strip in the water a good 4 minutes.

I just find it hard to believe my salt level would still be the same as before my sand filter was leaking.

 

[dravenone]

I have left the strips to soak for a few minutes and up to almost an hour. I get the same result as long as they have been left to soak long enough. the bar never goes dark for me in the time the instructions say.

 

[mickey4paws]

Thanks, Dravenone, I appreciate it.

 

[polyvue]

After hearing how accurate these strips are, I purchased them, in the hope of verifying the readout on my GoldLine Aqualogic SWG. Unfortunately, the strips consistently test far above the sensor -- e.g. if the Aqua Logic controller reports 2800 or 2900 ppm, the strips indicate 3660.

I've monitored this disagreement for many months at various salt levels, water temperature, etc., but the strip test invariably reports the sodium chloride at 500-800 ppm higher than the SWG.

Not sure which is correct, but as the Aqua Logic controller would cut off chlorine generation if it sensed an excessive amount of salt (which it does on occasion in the minutes when salt is first added to the pool) and is also happy to stop chlorine production when it determines that the salt level is inadequate, I've elected to ignore the test results and believe the sensor.

 

[Bama Rambler]

Here's one post that talks about why it might read low. calibrating-an-aqua-rite I know it's for an aqua-rite but I believe the same would apply to an Aqua-Logic.

 

[duraleigh]

polyvue,

I don't have a salt pool but judging from what many others have posted over the years, I think your strips are more accurate than the sensor.

 

[kjcole]

Leaking won't lower salinity since the salts are dissolved (take a bucket of water out of the ocean, pour half the water out of the bucket - do you expect the salinity of the remaining water in the bucket to change?). Evaporation and dilution (rain, fill water) will change salinity.

 

[polyvue]

Here's one post that talks about why it might read low. calibrating-an-aqua-rite I know it's for an aqua-rite but I believe the same would apply to an Aqua-Logic.

There's seems to be lots of different thinking about this. In the thread, Mark (mas985) states:

The so called "Calibration" for Goldline units is not really a calibration at all. The only thing is does is replace the average salt level with the instaneous salt level. Nothing more.

Mark also says

they want to make sure there is enough salt in the water so I believe that they put an offset in the reading to account for other dissolved solids which is why the unit usually reads on the low side if you happen to have low dissolved solids other than salt.

which strikes me as topsy-turvy (I have very high TDS 5000+ so expected the opposite effect.)

This topic was explored in some depth in 2006 at PoolForum (see http://www.poolforum.com/pf2/showthread.php?t=4655) A number of posters warned against relying on Aqua Check Test Strips, preferring the Taylor K-1766 drop test for accuracy.

According to an adminstrator in this post (http://www.poolforum.com/pf2/showthread.php?t=4655&page=2) the precision of the drop test performed by an individual may be +/- 400 ppm, which, if true, makes any concern about a discrepancy between the test and the SWG reading (that falls within this range,) moot.

Lastly, I understand that when the voltage in a SWG begins to creep up from baseline (my Goldline Aqua Logic cell voltage default is ~23.45) this may indicate calcium scale, which may or may not be visible. My takeaway is this: A. Clean the cell w/muriatic acid and water solution and B. Buy and use the Taylor drop test in lieu of test strips.

 

[JasonLion]

The Taylor drop test and the AquaChek salt test strips have almost the same precision, but the Taylor test is more difficult to perform. The main disadvantage of the test strips is that they can go bad if they get damp, and it isn't always possible to tell that this has happened. The Taylor test does not have that problem. The meters used in SWGs are far less precise.

On the other hand, it really doesn't matter what the salt level really is, as long as the SWG is happy with it. Way too many people spend lots of effort trying to figure out what their salt level "actually is", which really doesn't matter. The one time it is nice to have an independent measurement of the salt level is when you suspect that the SWG is broken and indicating low salt when the salt is actually high.