I have a question regarding the accuracy of the Aquacheck strips for salt. I have a new plaster pool and just recently added the salt and started the swg. I have a aquarite generator and the pool is approximately 16,000 gallons. So according to everything I read I needed to add 440-450#'s of salt initially and thats what I did. The swg has been working great and I have been adjusting it and my run time to keep it at 4ppm. The display shows between 3200 and 3400ppm while its running and a few times 3100ppm. I bought the salt test strips to verify my level and got a reading of 4500ppm on 2 seperate test days! So I am not sure what to do at this point. I was thinking of buying a refractometer to test it or just leave it alone. I dont want to do any damage to the swg or pool. Any suggestions would be greatly appreciated.
salt level and accuracy
- Thread starter gregs
- Start date
There has been discussion about the accuracy of the AquaChek salt test strips in this thread. If you wanted a different test to double-check, then you could get the Taylor K-1766 drop-based salt test. For greater accuracy, use the 25 ml line on the tube and multiply the number of drops by 80 ppm/drop.
It appears you may not have provided for the salt content that was in the pool prior to your addition.
440 lbs in a 16k pool adds 32-3300ppm......you already had some existing salt in there
440 lbs in a 16k pool adds 32-3300ppm......you already had some existing salt in there
Though I initiated the recent discussion on this topic in the thread mentioned by chem geek there are prior discussions that go back a few years... all of them that I had an opportunity to read are just as inconclusive as the one I began.gregs said:
My takeaway so far is that Aqua Chek salt test strips may be overstating the salt level, in some cases by a substantial margin, for pool water that has high Total Dissolved Solids (TDS). I purchased the Taylor K-1766 drop test (sodium chloride) in order to corroborate both my SWG reading and the Aqua Chek salt strips, and found that the drop test result and the SWG were in agreement; the salt strip test result was the outlier. At this point, I don't know why this is the case. If you're not having a problem with chlorine generation, leave well enough alone! Or buy the Taylor K-1766 to verify. :-D
EDIT To be clear, I'm not stating categorically that the Aqua Check salt test strips are inaccurate. It is my opinion that they may be inaccurate under certain circumstances. This remains an open question. END EDIT
- edited by Greg 10/11/2009 7:22 PM PDT
Would having a low TA level be a possible reason for the swg to work with a high salt level? My TA was around 50 so I added some baking soda per the pool calculator to raise it to 70. And my CYA was also still low at around 60 so I added per the calculator to bring it up as well. Later in the day I checked the swg and for the first time it shut down do to a HI salt reading. Any ideas?
I'm not absolutely convinced you have a high level of salt, but either way you can't ignore the SWG's shutting down no matter what the actual ppm level. This has happened once or twice with my SWG -- usually right after I add salt, and it corrects itself after the pump runs awhile. You might try cycling the the power to the pump (turning it off for a few minutes) and if that doesn't work, try resetting the Check System light and cycle the power once again. I don't remember if this has happened when I've added CYA or bicarbonate of soda. (My TA is around 70-75 ppm; the CYA is 50-60 ppm.) Do you know what the current reading (per your SWG) of salt is? If it's not displaying, switch to the Diagnostic menu and run through the various display modes... it should be available there.gregs said:
Pool Clown
In The Industry
If you want accurate, you should go with a digital salinity tester (+/- $100.00). I realize that will buy a lot of aspirin. But on the other hand, a diluting of the pool may be averted, saving the cost of water therefore paying for the unit!
just a clown talking... Ignore him.
just a clown talking... Ignore him.
I was looking around at other ways to test salinity and thats when I ran across the refractometer. There are various devices for use in salt water aquariums that may work but I am nut sure, but the refractometer seemed fairly accurate for the price.
I think the display reading was at 3500-3600 before it shut down. I was thinking that raising the TA may have changed the conductivity of the water and caused the swg to get a higher reading. It was also several hours after I had added the CYA and baking soda.
The pool is new and has only had chlorine and bleach added for the first 30 days so I wouldnt think that would have added much to the salt level.
Both times I took a reading with the strips I got the same readings at the "peak" of 4500ppm. The reading at the area where the base of the peak starts is 3800ppm.
I think the display reading was at 3500-3600 before it shut down. I was thinking that raising the TA may have changed the conductivity of the water and caused the swg to get a higher reading. It was also several hours after I had added the CYA and baking soda.
The pool is new and has only had chlorine and bleach added for the first 30 days so I wouldnt think that would have added much to the salt level.
Both times I took a reading with the strips I got the same readings at the "peak" of 4500ppm. The reading at the area where the base of the peak starts is 3800ppm.
- May 3, 2007
- 16,815
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
I have both the strips and a drop kit. The drop kit matches the SWG fairly closely within +-100ppm but the strips always read higher by 500 ppm. I no longer trust the strips.
I have also had nearly perfect agreement between the AquaCheck salt test strips and the Taylor drop test (tricky to do but very good when used correctly) across a number of bottles of salt test strips There have been occasional reports of AquaChek salt strips reading way off, but most people have very good results.
It is extremely common for the digital testers built into SWGs to be way off.
Electronic salt testers can drift substantially over time. If you are using an electronic salt tester make sure that it has been calibrated recently.
Most refractometers are not very precise in the range used by swimming pools. They are normally optimized to measure salt levels closer to ocean water, ten times as much salt as you use in a swimming pool. There are some better ones out there that can precisely measure lower salt levels, but they tend to be expensive.
In this particular case, it really doesn't matter. Both the pool and the SWG will be fine with salt anywhere from 3,000 to 4,500. As long as the SWG is happy with the salt level and it is producing chlorine, then leave things alone and don't worry about it.
The SWG is measuring the resistance of the water to electricity, which normally corresponds to the salt level fairly closely. However, there are a couple of other factors that can affect the resistance, which can cause the reading to differ from the salt level. What really matters to the SWG is the resistance, not the true salt level. So, if the SWG resistance based measurement comes out in a range the SWG is happy with, the true salt level really doesn't matter.
The situation is a bit more complex when the SWG is measuring an invalid salt level, the salt level might be wrong, or the sensor could be broken. But you don't need to worry about that case, since the SWG is reading a good salt level.
It is extremely common for the digital testers built into SWGs to be way off.
Electronic salt testers can drift substantially over time. If you are using an electronic salt tester make sure that it has been calibrated recently.
Most refractometers are not very precise in the range used by swimming pools. They are normally optimized to measure salt levels closer to ocean water, ten times as much salt as you use in a swimming pool. There are some better ones out there that can precisely measure lower salt levels, but they tend to be expensive.
In this particular case, it really doesn't matter. Both the pool and the SWG will be fine with salt anywhere from 3,000 to 4,500. As long as the SWG is happy with the salt level and it is producing chlorine, then leave things alone and don't worry about it.
The SWG is measuring the resistance of the water to electricity, which normally corresponds to the salt level fairly closely. However, there are a couple of other factors that can affect the resistance, which can cause the reading to differ from the salt level. What really matters to the SWG is the resistance, not the true salt level. So, if the SWG resistance based measurement comes out in a range the SWG is happy with, the true salt level really doesn't matter.
The situation is a bit more complex when the SWG is measuring an invalid salt level, the salt level might be wrong, or the sensor could be broken. But you don't need to worry about that case, since the SWG is reading a good salt level.