TDS Meter - The Planted Tank Forum
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post #1 of 9 (permalink) Old 04-03-2019, 06:02 PM Thread Starter
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TDS Meter

Finally, I decide to get a TDS meter. Could anyone please tell me is it ok to just buy one? Do i need the calibration liquid right away? How can i know that the meter is accurate? Thank you!


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post #2 of 9 (permalink) Old 04-03-2019, 07:50 PM
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If you want to know if the meter is accurate, and it doesn't come with calibration solution, then you need to purchase it. They *should* be calibrated straight from the factory but sometimes they don't always match up. One TDS meter should be fine although some people do have two or more. If they are different models, it's not unheard of for them to give different results, even if they are all calibrated using the same brand TDS calibration solution.
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post #3 of 9 (permalink) Old 04-04-2019, 05:26 AM
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I just checked mine with distilled water... It read 001

as far as I'm concerned it must be accurate.

Yeah... I name my fish...
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post #4 of 9 (permalink) Old 04-04-2019, 07:51 PM
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Calibration solutions at 342ppm or 1,000ppm are going to be more accurate than distilled or RO water will be. You can have two TDS meters that read about the same at lower TDS values, but higher TDS values could vary widely.
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post #5 of 9 (permalink) Old 04-04-2019, 10:12 PM
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As @Zoidburg said, you really need the 342 ppm calibration solution to correctly calibrate. If you want to double-check that the 342 solution is, in fact, calibrating it correctly, you can do this:

1) Get some, e.g.; KHCO3 (or any fert salt).
2) Use the Rotala Butterfly | Planted Aquarium Nutrient Dosing Calculator calculator and pick a target dKH for one gallon of distilled or RO water. Maybe 8 dKH (easier to measure dKH at higher numbers).
3) For this example, it returns 1.08 grams in 1 gal of pure water = 174 ppm of HCO3 and 111 ppm of K.
4) Add the 1.08 grams to the pure water (assumes your scale is calibrated, which is another story) and make sure it's dissolved well.
5) Sum the ppm numbers, which will return 285 ppm.
6) Stick your TDS pen in the gallon of water and you should get something very close to 204 ppm (if using a 0.5 conversion factor TDS meter - most US TDS meters) or 285 ppm (if using a 0.7 conversion factor TDS meter). Also, take a KH reading to see if you're close to 8 dKH just as triple-check.

Any of the above variables can be substituted with different salts and concentrations to double-double-double-double and double-check to your hearts desire.
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Last edited by Deanna; 04-11-2019 at 07:24 PM. Reason: Clarify
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post #6 of 9 (permalink) Old 04-12-2019, 01:00 PM Thread Starter
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TDS Meter

Ohhhh it seems to be more complicated than i thought. Im getting one and perhaps will need to ask you all for questions. Thank you so much for the input!


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post #7 of 9 (permalink) Old 04-14-2019, 01:09 PM
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Ohhhh it seems to be more complicated than i thought. @novv
Not really. You asked about how you could confirm that it was reading correctly and that is where it it gets somewhat involved. However, the calibration solution is cheap and easy to use. Once you calibrate the meter with it, you shouldn't need to worry about verifying the meter by going through all the testing I mentioned.

When buying it, just decide if you want one that is based upon a .5 or .7 conversion factor (see the manufacturer's specs). Most that are sold in the US use the .5 factor, but that won't give a reading close to actual ppm values unless you use a calculator such as this: https://www.translatorscafe.com/unit...-conductivity/. My preference is for the .7 factor meters.

In any case, most of us use the TDS meters as an indexing tool, so the conversion factor doesn't matter that much. You stick it in your tank, get a reading, and then just compare that reading to future readings in order to gauge if the tank is performing to your expectations.

Last edited by Deanna; 04-14-2019 at 01:43 PM. Reason: Add
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post #8 of 9 (permalink) Old 04-15-2019, 04:52 PM
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Quote:
Originally Posted by novv View Post
Finally, I decide to get a TDS meter. Could anyone please tell me is it ok to just buy one? Do i need the calibration liquid right away? How can i know that the meter is accurate? Thank you!
Most of them are calibrated as NaCl equivalent. Calibration solution is easy to make at home with demineralized water and any kitchen salt. After the first verification or calibration the value doesnt shift like pH probes do. Though sometimes the electrodes get dirty and can be cleaned by letting the meter sit in vodka overnight.

How to calibrate or verify TDS & Conductivity meters?

Calibration & verification of TDS and Conductivity meters can be done with kitchen salt.

Read RO water
Dissolve 3.0 grams of kitchen salt in 1000 ml RO
Take 100 ml
Add 900 ml RO water into the 100 ml
Read salt solution

Result = salt solution RO water

Expected readings

300 ppm as NaCl
318 ppm as KCl
419 ppm as 442
614 S



Test can be done with kitchen iodized salt, pickling salt or sea salt dissolved in distilled or RO water.

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post #9 of 9 (permalink) Old 04-17-2019, 04:12 PM Thread Starter
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@Edward thank you so much! I hit the meter yesterday (ordered online) and it has no way to calibrate it. :/


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