# TDS tester



## hypnogogia (13 Jan 2022)

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
				









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					www.hannainstruments.co.uk
				




Any advice gratefully received.


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## MichaelJ (13 Jan 2022)

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


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## Maf 2500 (13 Jan 2022)

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)


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## dw1305 (13 Jan 2022)

Hi all, 


Maf 2500 said:


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


<"Multiply by 0.64">.


Maf 2500 said:


> 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


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## hypnogogia (13 Jan 2022)

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.


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## MichaelJ (13 Jan 2022)

Maf 2500 said:


> 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.



dw1305 said:


> <"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


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## Maf 2500 (13 Jan 2022)

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.


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## brhau (13 Jan 2022)

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.


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## hwscot (13 Jan 2022)

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?


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## Ria95 (14 Jan 2022)

Maf 2500 said:


> 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.


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## MichaelJ (14 Jan 2022)

hwscot said:


> Are they a waste of money?


If inaccurate then Yes otherwise No


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## Djoko Sauza (14 Jan 2022)

hwscot said:


> 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.


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## MichaelJ (14 Jan 2022)

Maf 2500 said:


> 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.


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## Maf 2500 (14 Jan 2022)

Ria95 said:


> 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.


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## Maf 2500 (14 Jan 2022)

MichaelJ said:


> 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


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## MichaelJ (14 Jan 2022)

Maf 2500 said:


> 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.


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## Maf 2500 (14 Jan 2022)

MichaelJ said:


> 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.


MichaelJ said:


> 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!


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## erwin123 (14 Jan 2022)

hwscot said:


> 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.


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## Nick potts (14 Jan 2022)

hwscot said:


> 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


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## MichaelJ (14 Jan 2022)

Maf 2500 said:


> 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.



Maf 2500 said:


> 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


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## medlight (14 Jan 2022)

This is the one I use and it is very good, it has temperature compensation which makes it very accurate.


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## AlecF (14 Jan 2022)

I had a cheap pancel which stopped working after 7 months as I couldn't;t see a way to replace the battery. It was a pair with a PH meter which became unreliable and I decided I didn't need. Now I use one of the cheaper HM. As other note these are a third of the price. I'm sure they may be less reliable. I understand that and feel I'm not seeking to do high order science and the hobby is already expensive.


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## dw1305 (14 Jan 2022)

Hi all,


MichaelJ said:


> 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).


I didn't know to be honest, I'd just assumed it would be 0.64, because <"that is the normal conversion factor for fresh water">.  

Personally I never use <"ppm TDS">, unless that is the unit I mean and I've actually evaporated a <"known volume of water to dryness"> and weighed the residue.

cheers Darrel


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## MichaelJ (14 Jan 2022)

dw1305 said:


> Hi all,
> 
> I didn't know to be honest, I'd just assumed it would be 0.64, because <"that is the normal conversion factor for fresh water">.


Neither did I until I started to look into it a while ago.  I suppose the TDS 442 standard (40% Na2SO4, 40% NaHCO3, 20% NaCl) that has been used for ages as a "natural fresh water standard" may not be as good a standard as the more stable KCl solution that is now the international standard for calibration of instruments used for conductivity measurements.

Cheers,
Michael


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## dw1305 (14 Jan 2022)

Hi all,


MichaelJ said:


> more stable KCl solution that is now the international standard for calibration of instruments used for conductivity measurements.


I've always used potassium chloride (KCl) for the <"calibration standards">. The secret is to make up a large volume <"fairly accurately"> and then only use each aliquot once. We will have some "442" calibration standard somewhere, but I've always made the calibration standards for the conductivity meters.

I don't this for the pH meters, <"we buy these">. The problem is that you get through a lot more buffer and they are much more complicated to make up.

cheers Darrel


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## hypnogogia (14 Jan 2022)

Have decided on this.  I figured to get one that reports in microsiemens and I can always convert to ppm if needed.






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					www.hannainstruments.co.uk


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## jaypeecee (14 Jan 2022)

hypnogogia said:


> I wonder if @jaypeecee also has a view?I seem to remember him mentioning tds meters as well.


Hi @hypnogogia 

Please take a look at:









						GH/KH for dummies
					

Hi @Jaceree,  Is Santa bringing you an HI-991301 then? o_O:rolleyes::D  Now, that's an expensive meter!  JPC  Thats one of the more pricey ones i found.



					www.ukaps.org
				




JPC


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## hypnogogia (14 Jan 2022)

@jaypeecee thank you. Looks like our posts crossed.  I pulled the trigger on the HI 98303.


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## jaypeecee (14 Jan 2022)

hypnogogia said:


> Have decided on this. I figured to get one that reports in microsiemens and I can always convert to ppm if needed.
> 
> 
> 
> ...


Hi @hypnogogia 

Yes, I also prefer to use electrical conductivity in microSiemens/cm.

You may also find the following chart useful. Can't beat a picture!



			https://www.astisensor.com/Conductivity_to_TDS_Conversion_Table.pdf?zoom_highlight=conductivity+tds+conversion#search=%22conductivity%20tds%20conversion%22
		


JPC


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## MichaelJ (14 Jan 2022)

erwin123 said:


> 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 said:


> 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





medlight said:


> This is the one I use and it is very good, it has temperature compensation which makes it very accurate.



Ok, here is a way to figure out if you saved _40 quid_ or wasted a _tenner:_

You will need a microgram scale, pure NaCl and 1 liter of distilled water (at room temperature say 21C).

1. carefully measure and add 0.1 gram of NaCl to 1 liter of distilled water at room temperature - stir it carefully and let the water settle. Measure and write down the TDS
2. Repeat step 1 three more times.

You should measure 100, 200, 300 and 400 ppm depending on your meters internal conversion factor.

Now, more importantly, If you can draw a _reasonable_ straight line between these 4 points then you're all good regardless of your brand, make or model of your TDS meter. If not, get a replacement 

Cheers,
Michael


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## Nick potts (14 Jan 2022)

MichaelJ said:


> Ok, here is a way to figure out if you saved _40 quid_ or wasted a _tenner:_
> 
> You will need a microgram scale, pure NaCl and 1 liter of distilled water (at room temperature say 21C).
> 
> ...


I have tested it with a calibration standard but wouldn't again, it is fine for my needs and saved me £40  

For what I use it for which is mostly making up RO water to a certain TDS it is fine, it doesn't have to be all that accurate even, but I think it is. Do we really need really expensive meters for general fish tank usage? I don't personally think so.


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## MichaelJ (14 Jan 2022)

Hi @jaypeecee,



jaypeecee said:


> Hi @hypnogogia
> 
> Yes, I also prefer to use electrical conductivity in microSiemens/cm.


Yes, me too. Unfortunately, not much in this hobby refers to uS/cm.



jaypeecee said:


> You may also find the following chart useful. Can't beat a picture!


Generally true, but not this this chart in particular. If your referring to the depicted curve, keep in mind that everything that is important to us in this hobby is in the 0-1000 uS/cm range - which is an indiscernible fraction of the beginning of this curve...

Cheers,
Michael


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## MichaelJ (14 Jan 2022)

Nick potts said:


> Do we really need really expensive meters for general fish tank usage?


No we don't. I have been a happy aquarium keeper for decades without owning a TDS meter for sure, but if your _deeper into_ the water chemistry bit, I merely suggest to make sure your measurement device(s) are honest with you - if you can find them cheaply thats just perfect. If you mix RO water and the quantities of carefully measured compounds you add to the water checks out with your TDS then you're very likely good to go 

Cheers,
Michael


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## jaypeecee (14 Jan 2022)

MichaelJ said:


> Generally true, but not this this chart in particular. If your referring to the depicted curve, keep in mind that everything that is important to us in this hobby is in the 0-1000 uS/cm range - which is an indiscernible fraction of the beginning of this curve...


Hi @MichaelJ 

I am fully aware of all the points that you have raised above. But, I was in the midst of replying to other posts at the same time. It was either that or not reply to your thread. Sorry if it fell short of what you were expecting.

JPC


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## MichaelJ (14 Jan 2022)

jaypeecee said:


> Sorry if it fell short of what you were expecting.


Not at all @jaypeecee ... just wanted to raise awareness of the fact that the curve, due to its scaling, doesn't represent anything relevant to our hobby - but of course I know that you know that.

Cheers,
Michael


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