Salt Test Issues

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savgerl

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Jul 29, 2015
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Atlanta, GA
Hi TFT, first post here - I'm usually a reader but I'm stuck on this one. Big thank you to everyone that answers all of the questions posted here. Best forum I've ever read!

I am just coming off an AA treatment. All is going well. Thursday will be the two week mark and no reappearance of stains and CL is holding.

Now I'm working to rebalance everything else and I'm having issues w/ my salt readings. Shortly after we reopened the pool (about three weeks ago), the salt level was within range albeit at the lower end (if memory serves me it was 2,500). The pump prefers 2,700-3,400 and I think will produce CL down to 2,200. Anyway I added some salt to get it up to preferable levels. Two days later I got a "low salt" error message on my Aqua Plus. It made no sense based on my prior tests and adding salt so I retested. AP said 2,500 but my K-1766 drop test said 3,500. I've always had a small delta (~200ppm'ish) but not one like this. I then dug out a TDS EZ meter and it read 2,700 (pretty close to the pump reading). Still not wanting to think my test kit could be off, I bought and tried the AquaCheck salt test strips. They also agreed with the pump.

I reached out to TFTestKits searching for any thoughts --- love !! --- and Rebecca helped me quickly replace my reagents (one of the two was probably past its prime). The postman probably thought I was crazy as I met him at the box to grab the new reagent and test but I needed to know! :) Retested with two new reagents for K-1766 --- still reading at 1,000ppm higher than the pump. Grrrr

Today I took the salt cell off to see if that was creating any issues. It was clear but I cleaned it anyways. Reran all tests (TF-100) and all salt testing options I have.

Temp - 73 (water has been ~63 since pool opening up until yesterday when it hit 70)
CL - 3.5
CC - 0.5
pH - 7.2
TA - 80
CH - 480
CYA - 60
Borates - 50
Salt:
Pump - 3,500
Test Strips - 3,630
TDS EZ - 2,990
K-1766 4,600

Other than AA and the salt mentioned above, I've added some stabilizer and a bunch of Calcium Hardness as I was running way low. During AA I used bleach to keep CL in line but did turn back on the SWG late last week. The last two days my need to add bleach has dropped so I'm pretty sure the SWG is producing CL, the reading is just so far off the drop test it has be puzzled. I'm also worried about having to keep salt levels 'inflated' to keep the pump happy.

If my salt level really is 4,600 does that hurt my pool or equipment?

Thoughts on why I'm getting such a variance between the pump and the drop test?
 
Welcome to TFP! Thanks for supporting the site!

Here are my thoughts on the matter.

If the SWG is happy and making chlorine then none of the rest of it matters. As long as it is operating properly. Salt tests are fickle beasts that are not particularly accurate, like +/- 300-400 ppm. So, add a few hundred ppm to one and subtract a few hundred ppm from the other and you are pretty close.

No, salt 4000-5000 ppm will not hurt anything in your pool. One year I listened to my low salt warning and added a few too many bags before I realized what cold water does for a salt reading in a SWG. It was well over 5000 ppm. My SWG shows high salt at 4600 ppm but continues to make chlorine. I didn't have to add salt for more than a year. :) For reference ocean water is about 35,000 ppm.

I use 4+ year old expired test strips to rest my salt a couple of times a year just to see if I am in the ballpark.

I do not trust my SWG below 70 degrees. I turn it off at 70, use bleach and don't turn it back on until it is above 70 again. This spring I had to add 4 bags of salt. I add one wait 2-3 days and turn on the swg, red light, repeat. I got a green light the afternoon after the third bag. The next morning it was red. Added another bag and it has been green since. I do this dance every spring.

Don't clean the cell if it isn't dirty it will shorten the cell life.
 
Your salt cell and TDS meter are not accurate measures of chloride (Cl-) content. They are simply electrical voltmeters that measure water conductivity. For an external TDS meter, you would need to calibrate with a standard solution in order for you to know if it is accurate. The same is true with your SWG.

The K-1766 is the truest measure as it is purely based on CHEMISTRY. There are no interferences or inaccuracies other than the concentration and volume of the titrant drops which is not likely to change unless you stored them improperly. Your chloride concentration is that which the K-1766 says it is (+/-200ppm).

Now, with that said, you must make the salt cell happy. HOWEVER, I would NOT add any salt until you are close to your normal swim season temperatures. The biggest mistake people make is believing their salt cell readouts when it is too cold and then dump a bunch of salt into the pool. Then, they've over-salted their pools and get high salt alarms later in the season.
 
The AquaRite cell does begin to report lower salt levels than accurate when the cell begins to fail. It could be that.

Also, make sure that you're differentiating between the "Average" salt display and the "Instant" salt reading. The instant reading is the salt level measurement right now whereas the average is the average of the most recent instant readings. If you've recently added salt, the average will lag behind for a while unless you reset it.

What are the readings in diagnostics?

Note: The AquaRite uses the performance of the cell to calculate the salt level. Therefore, it is chloride specific. It does not use a conductivity sensor like many of the other units.
 
Thank you JoyfulNoise and JamesW

It has been a few days since I added salt so the average and instant are only off by 100ppm. Average was 3400 and Instant was 3500.

Are you asking for other numbers in Diagnostics? I can get those and post in the am.

Is there a way to 'test' if the cell is going bad? It was replaced July 2013, so not quite at the 3-yr mark.
 
The best way to test an AquaRite is to compare the salt reading from the box to a known good test. The AquaRite uses the performance of the cell to determine the salinity.

The AquaRite and the AquaPlus know how much chlorine the cell is producing and it knows the water temperature. The box knows how much chlorine is made by a good cell at every water temperature and salinity combination.

Since the water temperature and chlorine production rate are known, the box can calculate the salinity.

However, as the cell begins to wear out, the chlorine production decreases and the box incorrectly calculates the salt level as lower than actual.
 
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