• You are viewing the forum as a Guest, please login (you can use your Facebook, Twitter, Google or Microsoft account to login) or register using this link: Log in or Sign Up
  • You can now follow UKAPS on Instagram.

TDS tester

hypnogogia

Member
Joined
6 Apr 2017
Messages
1,005
Location
Oxfordshire
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:



Any advice gratefully received.
 

MichaelJ

Member
Joined
9 Feb 2021
Messages
1,690
Location
Minnesota, USA
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
 

dw1305

Expert
UKAPS Team
Joined
7 Apr 2008
Messages
13,818
Location
nr Bath
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

Member
Thread starter
Joined
6 Apr 2017
Messages
1,005
Location
Oxfordshire
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.
 
Last edited:

MichaelJ

Member
Joined
9 Feb 2021
Messages
1,690
Location
Minnesota, USA
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.

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
 
Last edited:

Maf 2500

Member
Joined
5 Jan 2021
Messages
218
Location
Slade Dingle
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

Member
Joined
10 Jul 2020
Messages
109
Location
San Francisco, CA, USA
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

Member
Joined
15 Nov 2021
Messages
61
Location
Montrose
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

Member
Joined
11 Aug 2021
Messages
72
Location
DE
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

Member
Joined
9 Feb 2021
Messages
1,690
Location
Minnesota, USA
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.
 
Last edited:

Maf 2500

Member
Joined
5 Jan 2021
Messages
218
Location
Slade Dingle
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.
 

MichaelJ

Member
Joined
9 Feb 2021
Messages
1,690
Location
Minnesota, USA
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

Member
Joined
5 Jan 2021
Messages
218
Location
Slade Dingle
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

Member
Joined
4 Mar 2021
Messages
849
Location
Singapore
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.
 

MichaelJ

Member
Joined
9 Feb 2021
Messages
1,690
Location
Minnesota, USA
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 :)
 
Last edited:
Top