Unexpected Very High Salt/TDS Reading

[mdublu]

I had a 0 reading on my CYA upon opening my pool and wanted to confirm with a pool store test to make sure that was correct in case my reagent was bad.

My readings upon opening 4/26/11 and before adding any chemicals were:
FC 6.5, CC 0, PH 7.4, TA 80, CH 250, CYA < 30

The pool guy that opened my pool 4/27/11 added 4 gallons of chlorine (because I forgot to call and tell him to add nothing because he always adds too much chlorine when he opens). I'm not sure if the chlorine was 10 or 12.5.

The pool store test 4/30/11 FC 1, CC 1, PH 7.4, TA 80, CH 200, TDS 5300
My 4/30/11 test after the pool store had FC over 20 (I gave up at 40 drops) AND my salt test strip agreed with the 5300 salt level the pool store guy told me. My last salt test last fall was 2500. I added 100 lbs or so of salt to get it up to around 2500 a few years ago so the water would not burn my eyes and throat.

The pool store guy said my salt was 5300 (his paperwork said 5300 was the TDS) and that I'll need to replace a bunch of water if my chemicals stop working. And of course that I should not be using the liquid chloine but the trichlor pucks and non-chlorine shock. (Using the Pool Calculator...I figure I would have had to add about 500 lbs. of salt or 25000 ozs. of chlorine to get my salt from 2500 to 5000 since tested last fall!)

I know the TDS is more than just salt and I know the FC was well above 1, so I'm inclined to not believe the pool store guy's numbers. But my salt test strip also read about 5300. I found this online: "The level of TDS in the pool is influenced by many factors; the chemicals we add to adjust the pH, chlorine, water hardness, alkalinity, dust, dirt, human waste, . . . all increase its level."

Because my pool has just been opened and we have had alot of storms, is it possible a large amount of my TDS are dust and dirt and also can the high chlorine level be throwing off the salt or TDS tests?

The pool looks great except for the larger than usual amounts of dust, dirt and catkins from my oak tree than I have had in the past. I'm think of just waiting, watching and testing for now.

Thanks,
Mark

 

[chem geek]

If you do not get rain overflow and do not backwash your sand filter very often, then you might not have much water dilution. Even so, a 2 ppm FC per day chlorine demand over 6 months would add a little over 600 ppm salt to the pool. If you also added Muriatic Acid, then that would add salt as well. So over a few years I could see the salt level climbing, but a rise of 2800 seems pretty high.

TDS is mostly salt and it would be unusual for dust and dirt to contribute very much to it since they mostly don't dissolve in the water and instead get caught in the filter.

 

[JasonLion]

Even if salt is 5300, that isn't a major problem. It is curious how salt got to that level, especially as you don't want the salt level going up any further than that. Still, if you need to live with your salt level at 5300, it doesn't present any significant issues.

Salt tests in general tend to have errors more than the other tests. The electronic meters often used by pool stores tend to drift out of calibration and some problems have been reported with the test strips as well. However, when the test strips and the meter agree with each other, it seems likely that the level is correct. Which is to say that they could both be wrong, but it is far more likely that they are both right than that they are both wrong in exactly the same way.

 

[swanny]

I am going out on a limb here as I don't have near the experience as chem geek or Jason.. The test strips I have for TDS would bleach out at a high enough FC level causing a false high reading. So the 20+ FC could be effecting the tests both at store and home ( Did they use the same type of test strip as you or an electronic meter? ). I would probably try and get my FC below 10 and re-test before doing anything drastic ( water replacement, ETC )

What side of town do you live in? I'm up in Fishers.

 

[mdublu]

Thanks all. I will just watch this high salt for now and re-test again every few weeks to a month going forward. If I keep getting these readings I will probably try longer and more often back flushes this season to see if I can get it down. I was not paying attention at the pool store to see what they used to test TDS--strip or other. I think I may try the taste test, too, when my FC gets down to see if it tastes salty just for the fun of it. I read somewhere that at 2500 a person would not taste the salt but at 5300 one would. I never tasted salt at the end of last season.

swanny, I am in Carmel near 146th and Gray road.

Mark

 

[JasonLion]

People vary in their salt sensitivity fairly widely. The average person can start tasting salt around 2800, but some people can taste salt much lower and others won't notice salt until it is much higher.

 

[chem geek]

There is also the Taylor K-1766 salt test you could try, though that's obviously more money to spend just to get confirmation. I would think that at the 5000+ ppm salt level that you would taste it, in spite of their being variability in such taste thresholds.