TDS tester

[hypnogogia]

I’m considering investing in a TDS tester. From my reading the Hanna instruments are often recommended, but I’m u sure as to which one, or indeed if there are others worth considering. I’ve found the following:

HI-98301 Pocket TDS Tester (0 to 2000mg/L)

<P>The HI-98301 is a rugged and reliable pocket-sized tester that offers quick and accurate readings of TDS and is ideal for testing in the field and the laboratory.</P> <P>This tester features an amperometric graphite electrode that provides better repea

www.hannainstruments.co.uk

HI-98302 Pocket TDS Tester (0.00 to 10.00ppt)

<P>The HI-98302 is a rugged and reliable pocket-sized tester that offers quick and accurate readings of TDS and ideal for testing in the field and the laboratory. </P> <P>This tester features an amperometric graphite electrode that provides better repeata

www.hannainstruments.co.uk

Any advice gratefully received.

 

[MichaelJ]

Hi @hypnogogia I am using this one. the 0-2000 ppm range is what you want. Highly recommended. Very precise. Be aware that the TDS conversion factor for this particular model is x 0.5 ... if you want to convert between TDS and uS/cm. All TDS meters, as you probably know, measures EC which in turn is converted to TDS by the probe.

Cheers,
Michael

 

[Maf 2500]

I am looking at these with a view to buying also. This one seems to have a better range for fishkeeping purposes as far as I can tell, (more sensitive) but it measures in microsiemens so you would have to do your own conversion.

Wonder if @dw1305 has an opinion on these?

HI-98303 Pocket Conductivity Tester (0 to 2000μS/cm)

 

[dw1305]

Hi all,

but it measures in microsiemens so you would have to do your own conversion.

<"Multiply by 0.64">.

This one seems to have a better range for fishkeeping purposes as far as I can tell........Wonder if @dw1305 has an opinion on these?

Yes that should be fine. You only need a low range meter and 2 milliS (2000 micro S.) is fine for a top level.

cheers Darrel

 

[hypnogogia]

Thanks @Maf 2500 and @MichaelJ . I wonder if @jaypeecee also has a view?I seem to remember him mentioning tds meters as well.

Is there a benefit in having one that converts to ppm? I notice that of the ones linked to, some report in micro Siemens, another in tds.

 

[MichaelJ]

I am looking at these with a view to buying also. This one seems to have a better range for fishkeeping purposes as far as I can tell, (more sensitive) but it measures in microsiemens so you would have to do your own conversion.

Wonder if @dw1305 has an opinion on these?

HI-98303 Pocket Conductivity Tester (0 to 2000μS/cm)

Unfortunately almost everything around in the hobby is referring to TDS. I wish it would be uS/cm instead for consistency.

For what its worth even popular dosing calculators such as the Rotala calculator states EC in TDS units as well.... and if your going with a device that uses a conversion factor of 0.5 its spot on.... 0.64 would be off.

<"Multiply by 0.64">.

As far as I am aware, none of Hannas TDS devices uses 0.64 ... only 0.5 (low range TDS) or 0.7 (higher range TDS). With some devices you can choose though.

Cheers,
Michael

 

[Maf 2500]

If the best conversion factor to use is 0.5 that makes it super easy to work out in your head. 0.64 is somewhat less convenient but is not far off two thirds.

I am just confused as to why the Hanna meters use a conversion factor of 0.5 if 0.64 is closer to the values we see in freshwater.

According to the WHO:

Total dissolved solids (TDS) is the term used to describe the inorganic salts and small
amounts of organic matter present in solution in water. The principal constituents are usually
calcium, magnesium, sodium, and potassium cations and carbonate, hydrogencarbonate,
chloride, sulfate, and nitrate anions.

Is there a table available anywhere that lists what the conversion factor is for each individual ion? To enable one to use a bespoke conversion factor depending on the types of ions that are present in the water in question.

 

[brhau]

A lot of folks also like the HI combo meter 98129. I use the HM Digital COM-100, which is about 1/3 the price. It reports conductivity in uS, and I just do the 0.64 conversion in my spreadsheet where I record readings.

 

[hwscot]

and there I was about to pull the trigger on one of those things you can get on amazon for less than a tenner. Are they a waste of money?

 

[Ria95]

If the best conversion factor to use is 0.5 that makes it super easy to work out in your head. 0.64 is somewhat less convenient but is not far off two thirds.

I am just confused as to why the Hanna meters use a conversion factor of 0.5 if 0.64 is closer to the values we see in freshwater.

Maybe this will help explain it further : 8 Common Mistakes When Taking Conductivity Measurements . In our application range the conversion is rather linear but you can find more precise factors here https://www.astisensor.com/Conductivity_to_TDS_Conversion_Table.pdf

For my applications I have been convinced by more intelligent people that there is no value in converting what is actually measured (EC) to an approximation parameter, likely with loss of information. I encourage you to get a meter that at least provides the EC value.

 

[MichaelJ]

Are they a waste of money?

If inaccurate then Yes otherwise No

 

[Djoko Sauza]

and there I was about to pull the trigger on one of those things you can get on amazon for less than a tenner. Are they a waste of money?

I got one of those for around 5 years now, still working fine.

 

[MichaelJ]

I am just confused as to why the Hanna meters use a conversion factor of 0.5 if 0.64 is closer to the values we see in freshwater.

0.5 is would be the correct conversion factor in a low range KCl solution ... which is more of a standard really ... call me boring, but I personally like the fact that if I mix 1 gram of NaCl into 1 liter of distilled water my Hanna reads ~1000 ppm ... which my HI-98301 actually does.

 

[Maf 2500]

Maybe this will help explain it further : 8 Common Mistakes When Taking Conductivity Measurements . In our application range the conversion is rather linear but you can find more precise factors here https://www.astisensor.com/Conductivity_to_TDS_Conversion_Table.pdf

For my applications I have been convinced by more intelligent people that there is no value in converting what is actually measured (EC) to an approximation parameter, likely with loss of information. I encourage you to get a meter that at least provides the EC value.

Thanks. I agree that EC is the best value to take note of for the reasons stated.

 

[Maf 2500]

0.5 is would be the correct conversion factor in a low range KCl solution ... which is more of a standard really

Yes, but if we are measuring a water with multiple types of ions why would we convert it based on KCl only? See post by Ria95

 

[MichaelJ]

Yes, but if we are measuring a water with multiple types of ions why would we convert it based on KCl only? See post by Ria95

Yes, I know the issues and how the conversion parameters are all over the place and depends on reference solutions That is why I don't like TDS as a measure and much rather have us all speak about EC in uS/cm terms... but everything in this hobby seems to evolve around TDS so I guess we just have to know our conversion factor when comparing "your TDS" to "my TDS"

Going back to the OP and my recommendation. It's all about precision and reliability. Hanna is at least one way to go. If you go with a meter that reads TDS know your conversion factor. Thats all.

 

[Maf 2500]

0.5 is would be the correct conversion factor in a low range KCl solution ... which is more of a standard really ... call me boring, but I personally like the fact that if I mix 1 gram of NaCl into 1 liter of distilled water my Hanna reads ~1000 ppm ... which my HI-98301 actually does.

Edited after I replied so needs another reply. Apologies for double posting. Yes I agree that would be satisfying but if that meter was probed into my tap water it would report the wrong ppm value because my tapwater is not an NaCl solution. That is why I was asking about the conversion factors.

Yes, I know the issues and how the conversion parameters are all over the place and depends on reference solutions Thats I why I don't like TDS as a measure and much rather have us all speak about EC in uS/cm terms... but everything in this hobby seems to evolve around TDS so I guess we just have to know our conversion factor when comparing "your TDS" to "my TDS"

Yes I agree that EC is a better metric. As it is consistent. It seems crazy that when we see a ppm measurement it could be as much as 28% out from what we think it is depending if the meter uses a 0.5 or 0.64 conversion factor. Or even more if it uses 0.7!

 

[erwin123]

and there I was about to pull the trigger on one of those things you can get on amazon for less than a tenner. Are they a waste of money?

I got a cheap China one but it actually works well. It costs so little, you can try it out (the experience I have had generally with this sort of stuff is that when you get a good sample, it actually is pretty good, its just that the QC is inconsistent)

If I test pure RO water, my meter reads 0ppm. Using my limited amount of maths/chem knowledge, I add Epsom Salt and/or Calcium Chloride to the RO water to achieve various ppm levels and the TDS meter is roughly +/- a few percentage points of the theoretical levels. So I would say, good enough for a tenner. For serious chemistry, obviously a few percentage points is unacceptable, but for aquarium use, I'm ok with it.

 

[Nick potts]

and there I was about to pull the trigger on one of those things you can get on amazon for less than a tenner. Are they a waste of money?

No, I have only ever used cheap <£20 TDS meters and have never had any issues.

I use on like this now Amazon product

It can show in ppm or uS/cm

 

[MichaelJ]

Edited after I replied so needs another reply. Apologies for double posting. Yes I agree that would be satisfying but if that meter was probed into my tap water it would report the wrong ppm value because my tapwater is not an NaCl solution. That is why I was asking about the conversion factors.

Totally true - but at least you would know the uS/cm. by multiplying by the inverse of the probes conversion factor and converting back to TDS using your favorite conversion factor.

Yes I agree that EC is a better metric. As it is consistent. It seems crazy that when we see a ppm measurement it could be as much as 28% out from what we think it is depending if the meter uses a 0.5 or 0.64 conversion factor. Or even more if it uses 0.7!

Yep! Its a total mess... its like everyone having their own definition of a meter