TDS

[KarlXII]

High TDS is often mentioned as a reason for changing water.

But how can you maesure it?

[hottub.pool_boy]

Have it tested at your nearest BioGuard pool / spa store or other who has the equipment.

[SerjicalStrike]

You can buy a test strip to test it.  

[Drewski]

The CHEAP and QUICK way:

Assume you have NICE and CLEAR water when the tub is OFF, everything is "balanced" with levels where they are supposed to be.

When you turn the tub ON (during the day) if you can't see the bottom, you have high TDS and it's probably time to change water.

Just my OPINION...

Drewski

[The_Bends]

TDS or Total Dissolved Solids is a measure of the total solids in the water. Solids in the water come from calcium, carbonates, dissolved organic and inorganic materials, salts from chlorine residue, swimmer waste, soluble hair and body lotion or anything placed in the spa that can be dissolved.

    It can be measured by strips, or a device designed to measure the electrical resistance of the water (less resistance, more solids).  

   It is important to change spa water regularly as the volume of water is much smaller than in a pool.  Just the same as putting sugar in a glass of water, eventually the sugar no longer dissolves and sinks to the bottom.  High TDS levels (above 1,500 ppm) reduces the efficiency of chlorine by 50% or more.  The water will have a dull appearance and a slightly salty taste.  

   

[Vinny]

TDS or Total Dissolved Solids is a measure of the total solids in the water. Solids in the water come from calcium, carbonates, dissolved organic and inorganic materials, salts from chlorine residue, swimmer waste, soluble hair and body lotion or anything placed in the spa that can be dissolved.

     It can be measured by strips, or a device designed to measure the electrical resistance of the water (less resistance, more solids).  

     

I hate to disagree with you but a TDS only measures conductivity in the water. Conductivity is the inverse of resistance. Just before you started posting I was looking at getting one and there's a post started by me and I believe drewstar gave a link that discusses TDS meters a little in depth.

What I found out is that a TDS meter will only measure stuff in the water that will move with electrical current (electrons). It seeks to measure how much stuff that has free electrons is in the water between 2 probes of alternating current.

So dead body cells or anything without free electrons will not show up but a charged particle (CL, CA and probably O3 (if there really is any present in the water   ))  and things like that will.

I was so close to buying a TDS meter too!

[Vermonter]

I hate to disagree with you but a TDS only measures conductivity in the water.  

Hi Vinny,

You are pretty much "right on" with that statement.  

I have a TDS meter that also measures conductibity, resistivity, salinity, temp (I think that's it).  To shift from "reading" TDS to "reading" conductivity, you change the mode and get a value - but that value is derived from a calculation (by the meter) based on a constant ratio and conversion factor.

TDS can be measured in other ways (typically, by measuring weight), but they aren't practical for the average hot tub owner.

I tracked my TDS (conductivity) a couple of times - but didn't find it to really be anything helpful in terms of my real-world decisions on when to change water.   I think approaches of a cange every 3-4 months (perhaps 6 months or more if you have light use) or a feel for how responsive your tub water is to your normal chemical dosing is equally valid and doesn't cost you anything.  Sometimes, in cold climates, changes are incorporate considerations for subfreezing conditions.

I also (long ago) did a comparison study on the amount of TDS addition that would result from using MPS according to Nature2 instructions vs. using dichlor (again, according to the "swap it" feature listed by Nature2).  The MPS approach contributed approximately 20 times as much TDS as did the dichlor approach (and, of course, the MPS does absolutely nothing for tub sanitizing).

TDS and Conductivity:

A bit more detail - for anyone interested - on TDS/conductivity

Total dissolved solids (TDS) is a commonly used measurement for fresh water (not salt water).  It is expressed in concentration units of milligrams per liter (mg/L) which is equal to part per million (ppm).  

To the best of my knowledge, ALL TDS meters rely on measuring conductivity and then converting it to "TDS".   That conversion is based on a ratio that is, in turn, based on using some standard ions (typically sodium and chloride, I believe) and then applying that ratio regardless of what the actual ion are (that are in your hot tub).  Since your hot tub will not contain "only" the ions used in the meter's calibration, the true TDS of your tub won't be measured - although it will likely be fairly close.

Unlike TDS, Conductivity is a direct measure of the concentration of the ions (dissolved) in the water you are testing.  Since it relies on the ability of the water (the ions in the water) to carry an electrical current, it will only measure ions present - not the dissolved substances that are not ions or that are nonconductive ions.  Conductivity typically does not pick up organic matter - which is certainly present in hot tub water based simply on human use and environmental contamination. It is usually expressed in units of either micromhos/cm or microsiemens/cm.

Bottom-Line:

If you really want to use TDS or conductivity as some type of operational guide for your tub, it can certainly be done.  I have never used test strips, so I can't comment on their accuracy or reliability - but TDS meters are readily availableand probably the general guideline of changing your water when the TDS reaches a point of 1500 - 2000 mg/L above your make-up water's TDS is OK.  Or you can establish your own TDS level at which you would change - again, based on your experience with your own tub.

Vermonter

[Vinny]

Vermonter,

Since you have access to more sophisticated test instruments than a  typical person might have, I understand how you can get a TDS accurately.

But if I bought a $20 or $100 TDS tester, it would only measure conductivity and convert it to TDS. If my pool, spa or any other body of water was contaminated by stuff that wasn't electically charged by nature - a non lab (or maybe even a lab) quality TDS meter won't cut it. The organic load of the water is totally being missed by it.

I agree that some criteria can be used but it seems that "electronically measuring" a tub for TDS is not the way, based on my limited research.

[Vermonter]

Vermonter,

Since you have access to more sophisticated test instruments than a  typical person might have, I understand how you can get a TDS accurately.
 

Acutally, my meter, even though a bit more than $100, measures conductivity and converts - which I had meant to point out more clearly than I guess I did.

I agree that some criteria can be used but it seems that "electronically measuring" a tub for TDS is not the way, based on my limited research.

Agree -  in my view, if you miss out on the organic and non-ionized portion of TDS, the value of any measurement, other than perhaps use as a trend indicator, is pretty marginal.

Vermonter

[Dr. Spa™ Ret.]

So for $20 - $100 you can get a rough/close idea, and for $10,000 you can get it exact?

I think close is good enough for me  

[Vinny]

So for $20 - $100 you can get a rough/close idea, and for $10,000 you can get it exact?

I think close is good enough for me  

I don't think you have any idea at that level ... my conclusion - just change the water 3 to 4 months depending on use!

[TN__HOT_TUB]

The CHEAP and QUICK way:

Assume you have NICE and CLEAR water when the tub is OFF, everything is "balanced" with levels where they are supposed to be.

When you turn the tub ON (during the day) if you can't see the bottom, you have high TDS and it's probably time to change water.

Just my OPINION...

Drewski

 

This sounds like my water.

Any solution other than changing the water?  Will shocking the water help?

[HotTubMan]

This sounds like my water.

Any solution other than changing the water?  Will shocking the water help?

A shcok could help. Perhaps a strong chlorine shock with the cover off for a good hour.

Your filter may be dirty or shot.

Your filter cycles (assuming you dont have a circ pump) may be too short. A Coleman has 2*3 hours cycles from the factory. A Hydropool has 2*2 hour cycles from the factory. These settings may not be aderquate for you and your family.

Presuming all of this is OK, and the water is still not good, DUMP IT.

[The_Bends]

Vermonter,

Since you have access to more sophisticated test instruments than a  typical person might have, I understand how you can get a TDS accurately.

But if I bought a $20 or $100 TDS tester, it would only measure conductivity and convert it to TDS. If my pool, spa or any other body of water was contaminated by stuff that wasn't electically charged by nature - a non lab (or maybe even a lab) quality TDS meter won't cut it. The organic load of the water is totally being missed by it.

I agree that some criteria can be used but it seems that "electronically measuring" a tub for TDS is not the way, based on my limited research.

You sound as if you would like  to get technical with the water,  have you worked out the saturation index of your water?  You don't have to buy a tester for that.  Since we know we should change the water at regular intervals, it could be a rough indicator for the basic quality of water (better for pools because you don't have to change the water as often if ever)

[Vinny]

I've calculated both indexes - Langlier and Hamilton and used a web based program to plug the numbers into.

The problem with those indexes is that they don't take TDS (at least from what I remember) into consideration.


I AM A TECHNICAL JUNKIE!!! - Anything technical, my family dreds it.