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TDS tester

medlight

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España
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

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15 Sep 2021
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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.
 

dw1305

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MichaelJ

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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
 

dw1305

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Hi all,
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

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

 

jaypeecee

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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!


JPC
 

MichaelJ

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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.
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

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
 

Nick potts

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Torbay
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
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.
 

MichaelJ

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Hi @jaypeecee,

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.

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
 

MichaelJ

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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

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21 Jan 2015
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Bracknell
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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