Pool Calculator and Salt

MeSue

LifeTime Supporter
Jul 29, 2007
345
Florida
I find Jason's Pool Calculator to be accurate on everything but salt. Last year when I first added salt to my pool, the pool calculator said I should need 6 bags. I added 4 and had already overshot my goal. Then this year when it needed topping off, it said I would need 60 lbs. I added 40 and was over my goal a bit. Just wondering if anyone else has had this experience? I'm pretty sure my pool volume estimate is pretty close because, like I said, all other chemical additions come out right based on the calculator. I use the Aquacheck test strips.
 

Strannik

TFP Expert
LifeTime Supporter
Jul 24, 2007
874
Brisbane, Australia
Can you post your numbers?

I've checked it against my calculator and it comes out the same (it would be a big surprise to me if it didn't because it's just simple calcs). Jason's calculator does round it to the whole pounds but it wouldn't make much difference (unless your water volume is really small like a bucket or something)
 

MeSue

LifeTime Supporter
Jul 29, 2007
345
Florida
I had 2150ppm before I added salt. Calculator said 60 lbs would take me to 3000. I added only 40, waited a day to test, and it showed I had 3260ppm.

Pool volume is in my sig.
 

JohnT

Admin
Mod Squad
TFP Expert
Apr 4, 2007
9,629
SW Indiana
You are showing double the increase you should. 40lbs should add 564ppm to your pool based on my own calculation. The calculator says it will add 560. Your increase was 1110ppm. The only way that can happen is an error in pool volume (and yours is right) or a testing error. What are you using to test? I'd bet you'd notice if the bags had increased to 80lbs!
 

MeSue

LifeTime Supporter
Jul 29, 2007
345
Florida
I'm using Aquacheck strips. Bought last year when I got the SWG. Maybe I got a bad batch?

My SWG does not give a salt reading--just low or high--it was giving the low salt alarm before adding the salt when my test showed 2150.
 

JohnT

Admin
Mod Squad
TFP Expert
Apr 4, 2007
9,629
SW Indiana
I've spent some time thinking about it, and I can't come up with any explanation that works. If the strips were wrong, they wouldn't show a reasonable reading at first, then show the increase wrong.

Water volume for an 18' pool is either 7600 at 4' depth or 8600 at 4.5' depth. Not enough error there to produce the numbers you are seeing.

What brand of salt are you using, and does it come in standard 40lb bags?
 

MeSue

LifeTime Supporter
Jul 29, 2007
345
Florida
It's Morton Pool Salt in the white bag with blue print. Says 40lbs / 18.1kg on it. The expiration date on my strips is May 2009 and I have kept them stored indoors. Very peculiar.
 

MeSue

LifeTime Supporter
Jul 29, 2007
345
Florida
No, it's been pretty dry here so no rain. I had topped off the water when we uncovered, but it was a day or two later when I tested for salt.
 

vincent

Well-known member
Jan 31, 2008
109
Malaysia
Sue, have your water been circulated enough? Or you can take a few more test from different location and depth to compare the results.
 

MeSue

LifeTime Supporter
Jul 29, 2007
345
Florida
Yep, I turned on the filter as soon as water was high enough and had it running 24/7 for a day or two before testing salt. I didn't put it on timer until after I did the second test because that was when I turned the SWG on.

Maybe something screwed up the second test... not sure what it could have been. Maybe I just didn't rinse the vial well enough after another test... who knows? Is it possible to leave the strip in the water too long for the salt test?

I have 4 strips left in this bottle. I probably won't test again right away since the SWG is running fine, but I might get another pack of strips for comparison next time.
 

Poolsean

TFP Expert
Apr 15, 2007
1,462
Ft Lauderdale, Florida
Remember too that the salt strips show a wide range so that 2150 may be 2300...all depending on the actual graduations on the strip you're using, and the bottle you're taking them out of. NEVER mix strips from one bottle to another. They are batched in lot numbers and the scales on the bottles can vary quite a bit from one bottle to another.

Strips are OK, but not the most accurate. If you've ever removed a strip while your fingers were wet, you may have contaminated the rest of the strips. Make sure your fingers are dry when removing strips, and close back the top afterwards.
 
G

Guest

Poolsean said:
ales on the bottles can vary quite a bit from one bottle to another.

Strips are OK, but not the most accurate.
I agree with this BUT they are much more cost effective than a hand held salt meter ( and I have come across many of them that are worthless. I only trust the Oakton/Goldine and the MyronL, and these DO need to be calibrated against a standard solution on a regular basis) and they have a far less chance of being used wrong than the salt drop test (chromate/silver nitrate titration) which is tricky, to say the least, to do properly!
IMHO, the salt titrator strips are the best way for the home user to economically test their pool.