Adding salt: why did my level go too high?

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Water_man

Water_man

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Jun 7, 2008
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Brookline, MA
This is my second season in "the program". After regular water adjustment and sanitation has become like a second nature, I decided this season to have top quality water by adding borates and salt, trusting positive reports from other users regarding these two chemicals in their proper dosage. I did a bucket test and couldn't taste salt at 3000 ppm.

I added borates to 50 ppm using the dosage calculated by Jason and chem geek (93 w% Boric Acid and 7 w% Borax.) I checked the level with LaMotte insta - test strips and I got it right.

I checked my pre-existing salt level with Aquacheck's salt test strips. I got 500 ppm. According to the pool calculator, adding 400 Lbs of salt should raise the level to 2634. However, after adding 400 Lbs I got 3820 ppm and I can certainly taste some salt. What happened?
 
Water_man said:
I checked my pre-existing salt level with Aquacheck's salt test strips. I got 500 ppm. According to the pool calculator, adding 400 Lbs of salt should raise the level to 2634. However, after adding 400 Lbs I got 3820 ppm and I can certainly taste some salt. What happened?
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You are usually better off adding partial doses then remeasuring when you need to add a lot. Half the first time and wait to measure the result, then half the remainder until you get a good handle on how much you need to add. In your case, I'd have added 200lbs, remeasured, recalculated the amount I thought I need to get where I wanted, then add half again. By then, you'd have a pretty good idea how much it was going to take to get right where you needed. The most likely problem would be a mis-estimation of the pool volume.
 
Water_man said:
All other chem additions came up right, based on the pool volume I have.
My pool volume couldn't be wrong by 52%, as implied by the different salt levels.
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How long did you wait before testing? Sometimes it takes a while before the salt fully mixes with the water. Wait a couple of days and check it again.
 
Well, 22,000 gallons is 183,480lbs of water. 400lbs of salt would add 2180ppm to 22K gallons of water. Math gets the same answer as the calculator.


Three options: Your pool really holds 14,400 gallons (unlikely). Original reading was wrong and it was really ~1600ppm (never used salt strips, so I don't know if it's possible to do it wrong), or you really added ~600lbs of salt. Not likely either unless you are a really bad counter :-D

We need a "Scratching My Head" smiley!
 
Maybe Diamond Crystal had a promo: "Buy a 40 lb salt bag and get extra 20 lb salt for free in the bag!" Who knows? It's very unlikely that I had 1600 ppm before the addition, and I definitely added 10 bags. The good news: Next season, after winter dilution, it will be perfect. :party:
 

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Water_man said:
Maybe Diamond Crystal had a promo: "Buy a 40 lb salt bag and get extra 20 lb salt for free in the bag!" Who knows? It's very unlikely that I had 1600 ppm before the addition, and I definitely added 10 bags.
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Are you sure you added 40 lb bags? Diamond Cryatal also makes a 60 lb bag. My local Lowes and Home Depot carries both sizes. In fact, I just bought 2 60 lb bags of Diamond Crystal.

If it's not a measuring error it's a testing error.
 
Still have the empty bags. 40 Lbs. What's the chance that a non SWG pool, that gets 25% dilution every year, will start before salt addition at 1600 ppm salt? It's an unsolved mystery. Maybe I should try another batch of salt measuring sticks. Instructions say "white peak". The bottom light strip that develops after 5 minutes is never white. It's light yellow. Will posting a pic of a developed strip be worthwhile?
 
It is possible to start with that much salt if the pool has been in operation for a while. If you have verified that they were 40 lb bags I would have to say that you did the salt test wrong the first time. Not an unusual thng for the first time doing a test. Use only 1 inch of water in a container, let the strip sit in it a minimum of 5 minutes until the bar at the top darkens and there is no more movement of the light strip over a 1 minute interval.
 
I experienced a similar situation this year. Started w/ ~1200 ppm salt (1170 my Aquachek test, 1200 pool store test with different water sample), added 160lb Diamond Crystal from Lowes (four 40 lb bags), tested 2 days later (today) and came up with 2830 ppm.

According to the pool calculator 160 lbs should have put me at 2300 ppm (17,500 gal). Although my calculation of the pool volume could be off slightly, it's definitely not 12,000- other chems behave as expected for 17,500 gallons. For me, the extra salt will end up being lost in backwashes, splash out, etc. so I'm not worried about it, just thought I'd chime in and say, me too. :-D
 

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