# affordable Tds pen.



## plantnoobdude (14 Feb 2022)

Hi, i'd like a tds pen preferably under 20 pounds. should i get one in microsiemens? or ppm. I have no idea about the conversion rates and stuff, what does it mean? and if you have some links to read up about it, I' greatly appreciate it! currently the best one seems to be a HM-tds-3


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## arcturus (14 Feb 2022)

plantnoobdude said:


> Hi, i'd like a tds pen preferably under 20 pounds. should i get one in microsiemens? or ppm.


Most measure TDS (in ppm) and conductivity (EC, in micro Siemens). EC would be preferable, but, unfortunately, most people use TDS...



plantnoobdude said:


> I have no idea about the conversion rates and stuff, what does it mean?


TDS is not a standard unit but a quantity. The different scales are a representation of the electrical conductivity (EC) in specific solutions (e.g. TDS 700 is based on KCl, TDS 500 on NaCl).

You really do not need to understand what EC and the TDS scales mean. What you need to know is which scale is your probe using. If the probe measures EC and TDS, then you can determine which TDS scale is in use (it will likely be TDS 500). After that, you just need to be careful not to be using TDS values in different scales. Different countries can use different scales and, often, the scale is not stated, so you have no idea which TDS scale was used, which can generate a large error in the reading...


plantnoobdude said:


> and if you have some links to read up about it, I' greatly appreciate it!


<TDS scales>.


plantnoobdude said:


> currently the best one seems to be a HM-tds-3


I have two cheap probes and a more expensive one and they all report the same values...


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## plantnoobdude (14 Feb 2022)

arcturus said:


> Most measure TDS (in ppm) and conductivity (EC, in micro Siemens). EC would be preferable, but, unfortunately, most people use TDS...
> 
> 
> TDS is not a standard unit but a quantity. The different scales are a representation of the electrical conductivity (EC) in specific solutions (e.g. TDS 700 is based on KCl, TDS 500 on NaCl).
> ...


Ugh my head is spinning, maybe ill try understand when I'm not half asleep!


arcturus said:


> No idea about the accuracy of these probes. But I have two cheap probes and a more expensive one and they all report the same values...


reassuring! thanks for the help.


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## plantnoobdude (15 Feb 2022)

so it is tds 500 (NaCl) I think Ill order it tomorrow the reviews seem pretty positive and it's quite affordable.


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## Sam66 (15 Feb 2022)

Have you seen this thread?





						TDS tester
					

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:  https://www.hannainstruments.co.uk/pocket-tds-tester-0-to-1999ppm-6710.html...



					www.ukaps.org


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## MichaelJ (15 Feb 2022)

Hi @plantnoobdude   A good TDS Pen is worth investing in... I use and recommend this one. Very accurate.  But you can get a cheaper one. Just make sure whatever you get has Automatic Temperature Compensation and you know the EC conversion factor which for this product is 0.5 (based on KCl which is  the International calibration standard)  - some are 0.64, some are 0.7.   The conversion factor is good to know, in case you want to compare notes with someone who also know their conversion factor or denote their conductivity in mS/cm and you want to convert that back to "your" TDS.

Cheers,
Michael


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## jaypeecee (15 Feb 2022)

plantnoobdude said:


> currently the best one seems to be a HM-tds-3


Hi @plantnoobdude 

I would advise against the above. If you look at the reviews of this meter on Amazon UK, my review may still be there. In a nutshell, the plastic membrane on the front 'panel' peeled away from the body of the meter after a few days' use. It would have readily allowed water to get inside it. Sadly, at this price, I wasn't surprised.

There has been a lot of recent discussion here on UKAPS about 'TDS' meters. Take a look around.

JPC


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## plantnoobdude (15 Feb 2022)

jaypeecee said:


> Hi @plantnoobdude
> 
> I would advise against the above. If you look at the reviews of this meter on Amazon UK, my review may still be there. In a nutshell, the plastic membrane on the front 'panel' peeled away from the body of the meter after a few days' use. It would have readily allowed water to get inside it. Sadly, at this price, I wasn't surprised.
> 
> ...


huh, odd most reviews seem pretty good. I really don't want to spend much on a tds meter and i'd rather spend it on plants lol. any other budget friendly options you know of? I wouldn;t like to spend ~50 pounds on a tds meter. maybeee 30. I'm also thinking of getting a cheap one on ebay and seeing if i luck out haha.


MichaelJ said:


> Just make sure whatever you get has Automatic Temperature Compensation


yes it does.


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## Nick potts (15 Feb 2022)

I have used this meter Charterhouse Aquatics: D-D TDS Meter and Digital Thermometer which is just a rebranded amazon one. Or the TDS-4 HM Digital TDS-4 Pocket-Size TDS Meter

My current one is also a very cheap one, it's not give me any problems so far.


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## jaypeecee (15 Feb 2022)

plantnoobdude said:


> huh, odd most reviews seem pretty good.


Hi @plantnoobdude 

Perhaps the manufacturers corrected the problem and recent reviews reflect this?


plantnoobdude said:


> I wouldn;t like to spend ~50 pounds on a tds meter. maybeee 30. I'm also thinking of getting a cheap one on ebay and seeing if i luck out haha.


It's essential that you can put your full trust in test equipment. It's false economy to do otherwise. At the very least, you will need calibration solution to check the accuracy of the meter from time to time.

JPC


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## jaypeecee (15 Feb 2022)

Nick potts said:


> My current one is also a very cheap one, it's not give me any problems so far.


Hi @Nick potts 

What do you use to check its accuracy? Was it supplied with any calibration solution? And, is it possible to adjust calibration if it's giving incorrect results?

JPC


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## plantnoobdude (15 Feb 2022)

Nick potts said:


> I have used this meter Charterhouse Aquatics: D-D TDS Meter and Digital Thermometer which is just a rebranded amazon one. Or the TDS-4 HM Digital TDS-4 Pocket-Size TDS Meter


now those are in my price range!


jaypeecee said:


> It's essential that you can put your full trust in test equipment. It's false economy to do otherwise. At the very least, you will need calibration solution to check the accuracy of the meter from time to time.


i can make my own right?


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## dw1305 (15 Feb 2022)

Hi all,


jaypeecee said:


> At the very least, you will need calibration solution to check the accuracy of the meter from time to time.


That is one of the advantages of conductivity meters, you can make your own <"conductivity standards">.


jaypeecee said:


> It's essential that you can put your full trust in test equipment.


I would most wholeheartedly agree with that. Personally I would want something like this <"HI-98311 EC, TDS and Temperature Tester, Low Range"> and then I would have peace of mind.


plantnoobdude said:


> I wouldn;t like to spend ~50 pounds on a tds meter.


<"Fifty pounds should buy you"> a budget <"low range meter">, something like the <"Primo 5">,  they are low maintenance bits of kit and much more robust than pH meters. It could (should) last ten years, so that is £5 a year.

cheers Darrel


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## erwin123 (15 Feb 2022)

I've tested my cheap china TDS pen by measuring RO water (pen reports RO water as 0ppm), and then adding Calcium Chloride / Epsom Salts and seeing whether the reading roughly matches theoretical expected values. And it appears to be correct, within a few percentage points.

For aquarium use, if my readings of my tank water are 120ppm -140ppm but in reality they are off by even up to 10%, I think its ok, for what I am using the TDS meter for, which primarily is (i) to check there are no strange fluctuations (which could indicate root tab leakage for example or some other problem) (ii) it is generally within TDS range 'recommended' by the internet for my shrimp.


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## arcturus (15 Feb 2022)

plantnoobdude said:


> now those are in my price range!


You can also buy two cheap ones from two actual different brands (and not the same rebranded device) and check if they read the same value 



plantnoobdude said:


> i can make my own right?


Yep, you can make your own KCl calibration solution or just buy a bottle of ready made calibration fluid. Check if there a calibration screw on the device; more expensive ones are usually calibrated electronically.


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## MichaelJ (15 Feb 2022)

erwin123 said:


> I've tested my cheap china TDS pen by measuring RO water (pen reports RO water as 0ppm), and then adding Calcium Chloride / Epsom Salts and seeing whether the reading roughly matches theoretical expected values. And it appears to be correct, within a few percentage points.
> 
> For aquarium use, if my readings of my tank water are 120ppm -140ppm but in reality they are off by even up to 10%, I think its ok, for what I am using the TDS meter for, which primarily is (i) to check there are no strange fluctuations (which could indicate root tab leakage for example or some other problem) (ii) it is generally within TDS range 'recommended' by the internet for my shrimp.


I very much agree with this pragmatic assessment of the situation.  If your device is accurate within 10% then it's actually pretty good.  Even if your chasing specific water for say breeding very soft-water fish its likely not going to matter if your TDS is 30 ppm, 25 ppm or 35 ppm...   and if your running a hard-water tank its definitely not going to matter if your TDS is 300, 270 or 330.

Of course, not everything will register as TDS (the compounds needs to carry a charge to do so), but the best general use of a TDS pen is being able to gauge the health status and maintenance level of the tank... If you're seeing TDS creep over time it's a good indication that you're not doing enough or large enough water changes or something is leaching into the water column, your dosing too much fertilizer (or not enough if you register an unanticipated drop over time) etc.  When I prep my WC water (with NPK,Ca,Mg) I always take the TDS to verify I am seeing the levels I am expecting.

I consider a reliable TDS meter just as important as a reliable thermometer.  

Cheers,
Michael


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## jaypeecee (15 Feb 2022)

MichaelJ said:


> ...but the best general use of a TDS pen is being able to gauge the health status and maintenance level of the tank... If you're seeing TDS creep over time it's a good indication that you're not doing enough or large enough water changes or something is leaching into the water column, your dosing too much fertilizer (or not enough if you register an unanticipated drop over time) etc.


Hi @MichaelJ 

Monitoring Conductivity/TDS is _definitely_ a wise thing to do and it's very cost-effective. But, it does rely on electrical conductivity changes of the aquarium water. However, an increase in organic waste would likely go undetected, wouldn't it? That's why I like to monitor ORP/Redox. Right now, the tank alongside me is showing +385mV. When all is well, it lies between +350mV and +400mV. In other words, no cause for concern at the moment. When organics build up, ORP/Redox goes down. I realize that very few freshwater aquarists use an ORP/Redox electrode but that's what makes me a geek!

JPC


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## MichaelJ (15 Feb 2022)

Hi @jaypeecee,


jaypeecee said:


> Hi @MichaelJ
> 
> Monitoring Conductivity/TDS is _definitely_ a wise thing to do and it's very cost-effective. But, it does rely on electrical conductivity changes of the aquarium water. However, an increase in organic waste would likely go undetected, wouldn't it?


It presumably depends on the waste, but TDS is definitely not the whole story - but its a good one nevertheless!  



jaypeecee said:


> That's why I like to monitor ORP/Redox. Right now, the tank alongside me is showing +385mV. When all is well, it lies between +350mV and +400mV. In other words, no cause for concern at the moment. When organics build up, ORP/Redox goes down. I realize that very few freshwater aquarists use an ORP/Redox electrode but that's what makes me a geek!


Yes, Oxidation-reduction potential is a good measure of the tanks ability to break down waste.  It might be an interesting thing for me to get an ORP meter  - It will give me something new to worry about and we can geek out comparing millivolt readings   Any recommendations that wont break the bank?        

Cheers,
Michael


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## fredi (15 Feb 2022)

Hanna HI-98301 is available on Amazon for just over £50 delivered to uk inc taxes
Bargain imho

​


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## MichaelJ (15 Feb 2022)

Hi @jaypeecee 


MichaelJ said:


> Any recommendations that wont break the bank?


I am thinking this one from Hanna HI-98120 ORP Tester ?

Cheers,
Michael


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## jaypeecee (15 Feb 2022)

MichaelJ said:


> It might be an interesting thing for me to get an ORP meter - It will give me something new to worry about and we can geek out comparing millivolt readings


Hi @MichaelJ 

Ah, that's brilliant! Finally managed to stop myself laughing!

I have a Milwaukee MW500, which is priced at just over £100.

JPC


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## jaypeecee (15 Feb 2022)

MichaelJ said:


> I am thinking this one from Hanna HI-98120 ORP Tester ?


Hi @MichaelJ 

It looks a nice piece of kit. May I suggest that you ask Hanna how well it copes with stray electric fields, which exist in the aquarium water column. This is particularly important with an ORP meter as the reading can take 15 minutes or so to stabilize. One alternative is to remove a water sample from the tank and test that.

JPC


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## MichaelJ (15 Feb 2022)

jaypeecee said:


> Hi @MichaelJ
> 
> It looks a nice piece of kit. May I suggest that you ask Hanna how well it copes with stray electric fields, which exist in the aquarium water column. This is particularly important with an ORP meter as the reading can take 15 minutes or so to stabilize. One alternative is to remove a water sample from the tank and test that.
> 
> JPC


Hi @jaypeecee  Well, thanks for that heads up... If none of that is a problem with the Milwaukee MW500 ? I might just get that - its 110 USD 

Cheers,
Michael


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## jaypeecee (15 Feb 2022)

MichaelJ said:


> Hi @jaypeecee Well, thanks for that heads up... If none of that is a problem with the Milwaukee MW500 ? I might just get that - its 110 USD


Hi @MichaelJ 

I'll PM you shortly.

JPC


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## plantnoobdude (15 Feb 2022)

now, let me see if i understood this correctly. my pen is callibrated from factory with NaCl (tds 500)
so if i make a solution of 500ppm Nacl then it should be 500ppm Tds? I went ahead and bought the cheap one anyway... hoping I'd luck out. I will ofcourse be testing it against a known standard
I'm guessing i should test/callibrate it against multiple solutions as well? i was thinking 100, 200, and 500. and if it's not reasonably accurate you guys can all have an, "I told you so" moment, and i'll be looking at ways to return the product!


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## MichaelJ (15 Feb 2022)

plantnoobdude said:


> now, let me see if i understood this correctly. my pen is callibrated from factory with NaCl (tds 500)
> so if i make a solution of 500ppm Nacl then it should be 500ppm Tds? I went ahead and bought the cheap one anyway... hoping I'd luck out. I will ofcourse be testing it against a known standard
> I'm guessing i should test/callibrate it against multiple solutions as well? i was thinking 100, 200, and 500. and if it's not reasonably accurate you guys can all have an, "I told you so" moment, and i'll be looking at ways to return the product!



Mine is fairly bang on in a pure NaCl solution.   Take 1000 ml of Distilled water add 100 mg of NaCl (and dissolve)  in increments of 100 mg  up to say 500 mg. (of course you need a good precision scale to do that)...  depending on the conversion factor you should ideally measure 100, 200, 300, 400, 500 ppm...  My HI-98301 is within 2-3% of these numbers.

Cheers,
Michael
​


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## plantnoobdude (15 Feb 2022)

MichaelJ said:


> Mine is fairly bang on in a pure NaCl solution.   Take 1000 ml of Distilled water add 100 mg of NaCl (and dissolve)  in increments of 100 mg  up to say 500 mg. (of course you need a good precision scale to do that)...  depending on the conversion factor you should ideally measure 100, 200, 300, 400, 500 ppm...  My HI-98301 is within 2-3% of these numbers.
> 
> Cheers,
> Michael


alright perfect! my scale is pretty good but not perfect. ill measre probably around ~5 g of salt and dillute it from there


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## MichaelJ (15 Feb 2022)

plantnoobdude said:


> alright perfect! my scale is pretty good but not perfect. ill measre probably around ~5 g of salt and dillute it from there


Yep that works!


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## plantnoobdude (20 Feb 2022)

hm tds-3 has arrived and it is quite accurate. it is within range of around 5ppm when using 100ppm solution, and around 10ppm when using 200ppm. it is always within 5% of callibration fluid. I think that amount can be my error and the tds pen is reasonably accurate. lets hope it lasts longer than it did for jaypeecee! apparently it has a three year warranty though.


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