Total Dissolved solids question.

Bwdonohues58

Gold Supporter
In The Industry
Apr 22, 2019
102
Homer, AK
OK. So I drained the entire pool (10,500 gallons) on April 1, 2021 and refilled it. After balancing the pool chemicals to the usual levels, I checked the TDS with a hand-held unit I bought from Hanna Instruments. As of April 7, it was 402. I check it every few weeks or so and it has increased gradually. Today it's at 1345. I have read some recommendations that if it goes above 1500, I should drain off half of the water and refill. This pool is not SWG. I only add Muriatic Acid for PH control and 12.5% liquid chlorine for FC. The folks at Clear Comfort have told me that the 1500 ppm is totally arbitrary and that I shouldn't do anything unless I notice any changes in the pool water. The pool water today (and always) is crystal clear and nobody is complaining. I am assuming that as LC and MA are added, the byproduct is NaCl or just salt. I'm just wondering if the folks at TFP have any opinions about this? Such as at what level of TDS should I consider a partial drain?
 

TexEdmond

Gold Supporter
Jun 16, 2021
512
Edmond, OK
Pool Size
25500
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
LC will contribute more to your salt content than MA will. If you're using the pool in a therapeutic setting, it might actually increase the comfort to your clients to let the salt content go higher. I've also read that manually chlorinated pools should target around half the salt concentration of SWG pools, but I don't think that's a hard-and-fast rule. Sorry no straight "yes/no" answer from me, but it seems like that's pretty wasteful draining half the pool then having to spend more on chems to rebalance just to control salt levels, which may or may not need to be kept artificially low.

Just curious, where did you read these recommendations to dilute when salt gets to 1500ppm? Is there anything in the local / state code that regulates this since you're a commercial pool?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,983
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
TDS is a meaningless parameter. I suggest you test for the components of TDS that matter. To you that is CYA (you do not add any), CH, and salt.
 

Bwdonohues58

Gold Supporter
In The Industry
Apr 22, 2019
102
Homer, AK
LC will contribute more to your salt content than MA will. If you're using the pool in a therapeutic setting, it might actually increase the comfort to your clients to let the salt content go higher. I've also read that manually chlorinated pools should target around half the salt concentration of SWG pools, but I don't think that's a hard-and-fast rule. Sorry no straight "yes/no" answer from me, but it seems like that's pretty wasteful draining half the pool then having to spend more on chems to rebalance just to control salt levels, which may or may not need to be kept artificially low.

Just curious, where did you read these recommendations to dilute when salt gets to 1500ppm? Is there anything in the local / state code that regulates this since you're a commercial pool?
There are lots of sites that say this. Here's one from In The Swim: Total Dissolved Solids in Swimming Pools | InTheSwim Pool Blog
This article says to keep the TDS under 2000, but there are lots of ones that say 1500.
 
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Bwdonohues58

Gold Supporter
In The Industry
Apr 22, 2019
102
Homer, AK
TDS is a meaningless parameter. I suggest you test for the components of TDS that matter. To you that is CYA (you do not add any), CH, and salt.
Thanks Marty, I would think that in my situation, the only thing that would cause the TDS to increase is salt. At startup in April, I put in the baking soda and calcium chloride and the TDS went from something in the 60's for tap water to about 400 when balanced. So I think the gradual increase is due to salt resulting from adding MA and liquid CL. My CH is consistently 200 and TA is always around 70-75. I definitely agree with TexEdmond that it's seems a waste to drain and add back just to lower the TDS. I also agree that a bit more salt probably makes the water more comfortable. The articles I have read say 1500, but the don't ever say why. Also, I just noticed from my Google search that many of these articles are written by pool service companies. I think that I will just leave things as is unless I notice some kind of change. Thanks again for your help.
 
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Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
10,848
NY
Also, I just noticed from my Google search that many of these articles are written by pool service companies
The same ones who’ll sell you the rebalance chems ? So they give you uneccessary stuff to throw you out of whack, Tell you to drain and then help you get back on track ? Yeah. So kind of them. You’re here now. As time goes on that only becomes more and more valuable. To both your time and wallet. :)
 
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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,983
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
but the don't ever say why.
Because they do not want to confuse the average pool owner with details, of which there are none to make any decisions based on TDS. The assumption is since you MUST be using trichlor, and if TDS rises it is primarily from CYA.

Our members are not average pool owners. All are exceptional pool owners, that understand details that effect their pool water chemistry.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
18,471
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
…. I'm just wondering if the folks at TFP have any opinions about this? Such as at what level of TDS should I consider a partial drain?

There is no rational correlation between TDS and draining a pool. Back in the old, old, old, olden days pool service techs had very limited chemical testing knowledge and equipment. In fact, they still do 😂. TDS was a way to measure the build up of permanent dissolved chemical species (assuming they affected conductivity) in the water. Old timers would say, “Your water is “old”, you need to dump it and start over … “. TDS would also correlate to higher probability of corrosion and so if the TDS was high they’d tell you you’re going to get equipment damage. But all of that is the equivalent of me licking my finger and sticking it up in the air then proclaiming I can give you the weather forecast for the next 10 days. Totally unreliable.

Stick with individual testing of chemical levels to determine how you should treat your water, not old-wive’s tales.
 

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