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TDS testing: Difference between revisions
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TDS stands for Total Dissolved Solids. It's an indicator of the overall mineral content of [[water]] | TDS stands for Total Dissolved Solids. It's an indicator of the overall mineral content of [[water]]; it does not provide information about the individual minerals present.<ref name=forston/> TDS testing is mainly useful for monitoring the effectiveness of a [[RO systems|RO purification system]] (whether the system is at home or in a store). It can also useful for monitoring changes in tap water because mineral levels can vary over time.<ref name=bsp>Briggs DE, Boulton CA, Brookes PA, Stevens R. [[Library|''Brewing Science and Practice.'']] Woodhead Publishing Limited and CRC Press LLC; 2004.</ref><ref name=water/><ref name=hob>Taylor DG. Water. In: Stewart GG, Russell I, Anstruther A, eds. [[Library|''Handbook of Brewing.'']] 3rd ed. CRC Press; 2017.</ref><ref name=brun>Brungard M. [https://www.brunwater.com/articles/tds-meter-do-you-need-one TDS meter: Do you need one?] Bru'n Water website. Accessed May 2022.</ref> For tap water, a [[water report]] is generally required to properly adjust it for brewing since the quantities of specific minerals needs to be known. TDS is usually expressed as parts-per-million (ppm), which is practically the same as milligrams per liter (mg/L).<ref name=ndsu/> | ||
TDS | TDS testing is conducted with a TDS meter, which is easy to use. It works indirectly: Dissolved salts (electrolytes) increase the electrical conductivity (EC) of water.<ref name=ndsu>[https://www.ag.ndsu.edu/publications/environment-natural-resources/using-electrical-conductivity-and-total-dissolved-solids-meters-to-field-test-water-quality Using electrical conductivity and total dissolved solids meters to field test water quality.] North Dakota State University website. 2019. Accessed May 2022.</ref> A TDS meter measures the EC, and then uses an equation to ''estimate'' the amount of dissolved solids.<ref name=brun/><ref name=ndsu/><ref name=water>Palmer J, Kaminski C. [[Library|''Water: A Comprehensive Guide for Brewers.'']] Brewers Publications; 2013.</ref><ref name=screwy>Feminella V. [https://www.thescrewybrewer.com/2014/07/pure-brewing-water-using-reverse-osmosis.html Pure brewing water using reverse osmosis.] The Screwy Brewer website. 2014. Accessed May 2022.</ref> This estimation is adequate for the purpose of monitoring a RO system, and determining whether the RO water is appropriately low in minerals to be used as a base for building a mineral profile. | ||
== TDS meters == | == TDS meters == | ||
There are a variety of TDS meters available. The | There are a variety of TDS meters available. The cheaper options tend to lack important features. | ||
{| class="wikitable" | {| class="wikitable" | ||
| Line 10: | Line 10: | ||
! Product | ! Product | ||
|{{Amazon|B07H578WWT|Dumsamker}} | |{{Amazon|B07H578WWT|Dumsamker}} | ||
|{{Amazon| | |{{Amazon|B09ZY2HNRR|Inkbird}} | ||
|{{Amazon|B007KDYOMU|HM AP-1}} | |{{Amazon|B007KDYOMU|HM AP-1}} | ||
|{{Amazon|B005IGXOK4|Bluelab}} | |{{Amazon|B005IGXOK4|Bluelab}} | ||
| Line 23: | Line 23: | ||
| Variable range ±1% | | Variable range ±1% | ||
| Variable range ±1% | | Variable range ±1% | ||
|- | |||
! ATC<sup>1</sup> | |||
|[[File:X-mark-16.png|alt=No|link=]] | |||
|[[File:Checkmark-16.png|alt=Yes|link=]] | |||
|[[File:Checkmark-16.png|alt=Yes|link=]] | |||
|[[File:Checkmark-16.png|alt=Yes|link=]] | |||
|[[File:Checkmark-16.png|alt=Yes|link=]] | |||
|[[File:Checkmark-16.png|alt=Yes|link=]] | |||
|- | |- | ||
! Calibration | ! Calibration | ||
|[[File:X-mark-16.png]] | |[[File:X-mark-16.png|alt=No|link=]] | ||
|[[File: | |[[File:Checkmark-16.png|alt=Yes|link=]] | ||
|[[File:Checkmark-16.png]] | |[[File:Checkmark-16.png|alt=Yes|link=]] | ||
|[[File:Checkmark-16.png]] | |[[File:Checkmark-16.png|alt=Yes|link=]] | ||
|[[File:Checkmark-16.png]] | |[[File:Checkmark-16.png|alt=Yes|link=]] | ||
|[[File:Checkmark-16.png]] | |[[File:Checkmark-16.png|alt=Yes|link=]] | ||
|- | |- | ||
! EC display | ! EC display | ||
|[[File:Checkmark-16.png]] (μS/cm) | |[[File:Checkmark-16.png|alt=Yes|link=]] (μS/cm) | ||
|[[File:Checkmark-16.png]] (μS/cm) | |[[File:Checkmark-16.png|alt=Yes|link=]] (μS/cm) | ||
|[[File:X-mark-16.png]] | |[[File:X-mark-16.png|alt=No|link=]] | ||
|[[File:Checkmark-16.png]] (mS/cm) | |[[File:Checkmark-16.png|alt=Yes|link=]] (mS/cm) | ||
|[[File:Checkmark-16.png]] (µS/cm or mS/cm) | |[[File:Checkmark-16.png|alt=Yes|link=]] (µS/cm or mS/cm) | ||
|[[File:Checkmark-16.png]] (µS/cm or mS/cm) | |[[File:Checkmark-16.png|alt=Yes|link=]] (µS/cm or mS/cm) | ||
|- | |- | ||
! Backlight | ! Backlight | ||
|[[File:Checkmark-16.png]] | |[[File:Checkmark-16.png|alt=Yes|link=]] | ||
|[[File:Checkmark-16.png]] | |[[File:Checkmark-16.png|alt=Yes|link=]] | ||
|[[File:X-mark-16.png]] | |[[File:X-mark-16.png|alt=No|link=]] | ||
|[[File:Checkmark-16.png | |[[File:Checkmark-16.png|alt=Yes|link=]] | ||
| | |[[File:X-mark-16.png|alt=No|link=]] | ||
| | |[[File:Checkmark-16.png|alt=Yes|link=]] | ||
|[[File: | |||
| | |||
|[[File:Checkmark-16.png | |||
| | |||
| | |||
|- | |- | ||
! Waterproof | ! Waterproof | ||
|[[File:X-mark-16.png]] | |[[File:X-mark-16.png|alt=No|link=]] | ||
|[[File:X-mark-16.png]] | |[[File:X-mark-16.png|alt=No|link=]] | ||
|[[File:X-mark-16.png]] | |[[File:X-mark-16.png|alt=No|link=]] | ||
|[[File:Checkmark-16.png]] | |[[File:Checkmark-16.png|alt=Yes|link=]] | ||
|[[File:Checkmark-16.png]] | |[[File:Checkmark-16.png|alt=Yes|link=]] | ||
|[[File:X-mark-16.png]] | |[[File:X-mark-16.png|alt=No|link=]] | ||
|- style="vertical-align: top;" | |- style="vertical-align: top;" | ||
! Notes | ! Notes | ||
| Battery is not replaceable. | | Battery is not replaceable. Dumsaker provides zero customer service; seller doesn't respond to messages. This meter is marketed under other cheapo brands as well. | ||
| | | 1-point calibration, but it resets randomly. | ||
| Digital 1-point calibration with 342 ppm NaCl. Magnetic body. | | Digital 1-point calibration with 342 ppm NaCl. Magnetic body. | ||
| Digital 1-point calibration with {{Amazon|B00Z6SJ69C|EC 2.77}} (2770 μS/cm). Displays icon for 30 days after calibration. Low battery indicator. | | Digital 1-point calibration with {{Amazon|B00Z6SJ69C|EC 2.77}} (2770 μS/cm). Displays icon for 30 days after calibration. Low battery indicator. | ||
| Digital | | Digital 1-point calibration with ''any'' calibration solution. Dual-range TDS & EC, which improves accuracy (can read TDS up to 19,990). Customizable TDS conversion factor. Adjustable ATC settings. Low battery indicator. Probe requires soaking before reading if it hasn't been used in a month. | ||
| Digital calibration (up to 3-point with 1413 µS, 12.88 mS, 84 µS). The 1413 µS & 12.88 mS calibration solutions are included. Tri-range TDS & EC, which improves accuracy (can read TDS up to 10,000). Fancy platinum black conductivity sensor improves accuracy and performance. Customizable TDS conversion factor. Adjustable ATC settings. Replaceable {{Amazon|B01GA9EID4|probe}}. | | Digital calibration (up to 3-point with 1413 µS, 12.88 mS, 84 µS). The 1413 µS & 12.88 mS calibration solutions are included. Tri-range TDS & EC, which improves accuracy (can read TDS up to 10,000). Fancy platinum black conductivity sensor improves accuracy and performance. Customizable TDS conversion factor. Adjustable ATC settings. Replaceable {{Amazon|B01GA9EID4|probe}}. | ||
|} | |} | ||
<sup>1</sup> ATC is | <sup>1</sup> ATC is Automatic Temperature Compensation. Conductivity is affected by temperature, and meters with ATC automatically adjust the reading to provide a standardized value (25°C). If the meter does not have ATC, the sample must be at 25°C (77°F) in order to provide an accurate reading. | ||
All of these meters also feature: | All of these meters also feature: | ||
| Line 80: | Line 80: | ||
Inline TDS probes for monitoring input and output of RO systems ''exist'', but there's no reason to believe they are accurate or worthwhile. | |||
== Usage == | == Usage == | ||
Using a TDS meter is simple: | Using a TDS meter is simple: | ||
# Let the system run for a sufficient period of time for the TDS to stabilize before taking a sample ( | # Let the system run for a sufficient period of time for the TDS to stabilize before taking a sample (typically around 1–2 minutes). | ||
# Put the meter's probe into the sample, swirl gently to remove bubbles, and wait for the reading to stabilize. | # Put the meter's probe into the sample, swirl gently to remove bubbles, and wait for the reading to stabilize. | ||
#* If you use a sample container, it needs to be clean and free of any mineral contamination.<ref name=bhfaq>[https://www.buckeyehydro.com/faq/ FAQ.] Buckeye Hydro website. Accessed May 2022.</ref> You can rinse the sample container two or three times with the water you intend to sample.<ref name=ndsu/> | |||
#* If your meter does not have ATC, the sample must be at 77°F (25°C). | |||
# After use, rinse the probe with purified water and/or dry it with a clean cloth. | # After use, rinse the probe with purified water and/or dry it with a clean cloth. | ||
== Calibration == | == Calibration == | ||
It's always wise to check that a measuring device is actually working as expected rather than taking the results just on faith.<ref name=ndsu/> Even if your meter isn't able to be calibrated, you can check the reading against a solution with known conductivity (a calibration solution) to verify that it is giving accurate results. Generally you should use a calibration solution with TDS near the range that you want to measure, although some meters require a specific TDS calibration fluid. | [[File:20ppm-calibration.jpg|thumb| Reading a 20ppm test solution to verify accuracy|alt=TDS meter reading 20ppm]] | ||
It's always wise to check that a measuring device is actually working as expected rather than taking the results just on faith.<ref name=ndsu/> TDS meters are known to drift and give inaccurate readings. Even if your meter isn't able to be calibrated, you can check the reading against a solution with known conductivity (a calibration solution) to verify that it is giving accurate results. Generally you should use a calibration solution with TDS near the range that you want to measure, although some meters require a specific TDS calibration fluid. | |||
;Buying a calibration solution | |||
Calibration solutions are available to purchase, although options are limited. Here are a few: | |||
*84 μS/cm solution available on {{Amazon|B01MR519M8}} | |||
*100 μS/cm and 1413 μS/cm solutions available on {{Amazon|B01F2OZY4U}} | |||
*700 μS/cm solution available on {{Amazon|B001VE99X8}} | |||
;Making a calibration solution | |||
You can make a calibration/testing solution yourself. For monitoring RO systems, we suggest using 18.7 mg/L NaCl (sodium chloride, table salt), which reads as 20 ppm TDS or 40 μS/cm.<ref name=forston/> | You can make a calibration/testing solution yourself. For monitoring RO systems, we suggest using 18.7 mg/L NaCl (sodium chloride, table salt), which reads as 20 ppm TDS or 40 μS/cm.<ref name=forston/> | ||
| Line 97: | Line 107: | ||
# Add 10 mL of the concentrated NaCl solution to 990 mL distilled water to make a 20 ppm TDS solution. Mix well. Discard the remaining concentrated solution. | # Add 10 mL of the concentrated NaCl solution to 990 mL distilled water to make a 20 ppm TDS solution. Mix well. Discard the remaining concentrated solution. | ||
# Take a TDS reading of the solution. If the reading is ''reasonably'' close to 20 ppm or 40 μS/cm, then the device is working correctly. Otherwise, the device should be calibrated per manufacturer instructions, if possible. | # Take a TDS reading of the solution. If the reading is ''reasonably'' close to 20 ppm or 40 μS/cm, then the device is working correctly. Otherwise, the device should be calibrated per manufacturer instructions, if possible. | ||
#* Note: If the meter does not have ATC, the sample must be at 25°C (77°F). | |||
The calibration solution can be stored in a sealed container for later use. | The calibration solution can be stored in a sealed container for later use. | ||
You can follow the same instructions above, but with a different amount of salt to make a calibration solution with a TDS tailored to your needs: | |||
{| class="wikitable" | {| class="wikitable" | ||
|+Calibration solutions<ref name=forston/> | |+Calibration solutions<ref name=forston/> | ||
| Line 123: | Line 134: | ||
| 1385 || 2770 || 142 g (for Bluelab meter) | | 1385 || 2770 || 142 g (for Bluelab meter) | ||
|} | |} | ||
== Cleaning == | == Cleaning == | ||
| Line 138: | Line 143: | ||
*[[Water report]] | *[[Water report]] | ||
==References== | == References == | ||
[[Category:Quality assurance and testing]] | |||