# TDS meter



## DutchMuch (Apr 12, 2017)

https://www.amazon.com/gp/product/B079DN9DRS/ref=ox_sc_act_title_1?smid=A1KZYDRXZIKJTQ&psc=1
this a good TDS meter?


----------



## mistergreen (Mar 3, 2007)

They're all pretty much the same. Go for it.


----------



## Maryland Guppy (Mar 5, 2015)

I have same meter.
TDS is good, think conductivity is a calculated amount.
Temps take a few seconds to adjust.


----------



## tiger15 (Apr 9, 2017)

Maryland Guppy said:


> I have same meter.
> TDS is good, think conductivity is a calculated amount.
> Temps take a few seconds to adjust.


It's actually the other way around. The meter measures electrical conductivity, and a fudge factor is used to convert conductivity to TDS. There is no direct measurement of TDS, which can only be determined in the lab by evaporating all water and weigh the solid left behind. The conversion to TDS is only rough approximation depending on what are the solutes. The fudge factor for seawater, for example, will be very different from hard fresh water dominated by Ca and Mg. Does your meter instruction say what is the default fudge factor, or there is an option to input your own.


----------



## mistergreen (Mar 3, 2007)

The meter's TDS guess work is a bit more accurate these days when they include a thermometer into it. The conversion factor is affected by temperature so you see a lot of these TDS meters also include a thermometer.

Side note. 
I use a duel stage carbon filter for my aquarium water mainly for dechlorinating. I just found out it also reduces the TDS by 40-50ppm.


----------



## DutchMuch (Apr 12, 2017)

Maryland Guppy said:


> I have same meter.
> TDS is good, think conductivity is a calculated amount.
> Temps take a few seconds to adjust.


ty  
if you got it I trust it lol


----------



## tiger15 (Apr 9, 2017)

mistergreen said:


> The meter's TDS guess work is a bit more accurate these days when they include a thermometer into it. The conversion factor is affected by temperature so you see a lot of these TDS meters also include a thermometer.
> 
> Side note.
> I use a duel stage carbon filter for my aquarium water mainly for dechlorinating. I just found out it also reduces the TDS by 40-50ppm.


It's not very accurate, even with temp adjustment. It depends on what are the sollutes. If it is largely organic, it can have very large tds, but little elevated conductivity.


----------



## DutchMuch (Apr 12, 2017)

tiger15 said:


> It's not very accurate, even with temp adjustment. It depends on what are the sollutes. If it is largely organic, it can have very large tds, but little elevated conductivity.


eh I didnt need a 100% accurate TDS meter for 100$
just wanted a suggestion on what other people are using.


----------



## tiger15 (Apr 9, 2017)

DutchMuch said:


> eh I didnt need a 100% accurate TDS meter for 100$
> just wanted a suggestion on what other people are using.


You can't get 100% accurate tds meter even if you spend $100,000, because it doesn't exist. The meter measures conductivity which is a proxy for tds. The one in the link appears to use a default fudge factor of 0.5, other brands use a different default factor.

I use this from eBay, cheaper with free shipping and a pH pen extra. It works essentially the same, except I can't even guess what fudge factor it defaults.

https://www.ebay.com/itm/Digital-LC...var=582376422933&_trksid=p2057872.m2749.l2649


----------



## DutchMuch (Apr 12, 2017)

tiger15 said:


> You can't get 100% accurate tds meter even if you spend $100,000, because it doesn't exist. The meter measures conductivity which is a proxy for tds. The one in the link appears to use a default fudge factor of 0.5, other brands use a different default factor.
> 
> I use this from eBay, cheaper with free shipping and a pH pen extra. It works essentially the same, except I can't even guess what fudge factor it defaults.
> 
> https://www.ebay.com/itm/Digital-LC...var=582376422933&_trksid=p2057872.m2749.l2649


was just a form of speech


----------



## Gerald (Mar 24, 2008)

The conversion factor from conductivity to TDS is about 0.50 for plain NaCl solution and about 0.67 for freshwater with a "typical" mix of other ions. So, a conductivity measurement of 100 uS corresponds to about 50 mg/L if NaCl is the majority of the dissolved material, or 67 mg/L in a freshwater sample containing an average mix of Ca, Mg, SO4, N, K, Cl, Fe, Mn, NO3, etc.

A chemically "accurate" measure of TDS (by evaporation and weight) is *biologically meaningless*, since it doesn't distinguish between the mineral ions essential for fish and plant growth and the dissolved organic compounds from wood and leaves. A sample could have high TDS (measured by weight) due to organics but have very few mineral ions. It's like measuring the nutritional content of your grocery shopping cart by weight.


----------



## tiger15 (Apr 9, 2017)

You don't need accurate measurement of TDS. You need consistent measurement of TDS. TDS meters are essentially conductivity meter. If one brand uses a factor of 0.5, and another brand uses 0.67. Comparison of TDS is no longer meaningful.

Conductivity or TDS is not a solute specific measurement like pH, NO3, NH3, PO4 . . . etc. It is a quick, proxy measurement of many parameters: salinity, hardness, osmotic pressure, level of pollution, or how long you haven't changed water. It's biological meaningful only if you can correlate TDS with the parameters you are interested in, and the measurement is consistent.


----------

