Cheap TDS meter?

Water analysis, treatment, and mineral recipes for optimum taste and equipment health.
violin_geek123

#1: Post by violin_geek123 »

Can anyone recommend a reliable and cheap TDS pen or meter? I'm only looking for a general ppm number for my brew water to check that it's in the ballpark after I make it (currently making batches of Rao/Perger with minerals and distilled water).
Brian Hong

mtbizzle

#2: Post by mtbizzle »

Perhaps a refractometer. They measure specific gravity, which I assume should be convertible into TDS? But I'm not sure. These are not digital devices, I'm not sure I'd trust a cheap digital device with fine accuracy here. You put the sample in and have to assess yourself. I'd be interested to hear if there is any refractometer or cheap option that coffee folks find reliable.

Although I'm not so sure that will be useful for assessing water - specific gravity should pretty much always be 1 :?

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homeburrero
Team HB

#3: Post by homeburrero »

I think you're looking for a conductivity meter, which are commonly available at very low prices. They simply measure the conductivity between two probes, and the conductivity of water is related to the dissolved electrolytes. Most of them display a TDS ppm value that roughly corresponds to the actual TDS but which can be off a lot depending on which minerals are in the water.

Google 'TDS Meter' and you'll see lots, like this one, beginning at prices below $20. They can be useful, with caveats, for some water testing purposes.
Pat
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Freddofl

#4: Post by Freddofl »

I got a 0-18% refractometer and it has been a huge help. I don't know that you can get accurate TDS out of it, but it's great to compare between shots. The only difficulty is that due to espressos turbidity the read out line is a bit fuzzy. It's fairly sharp and accurate if you use it on brewed coffee or an americano though.

This is the one I got: https://www.amazon.com/dp/B07KS221PM

I chose this one because a typical 2:1 shot will usually fall between 10 and 12% Brix which converts to about 17-20% extraction yield.

Edit: I just realized I misunderstood your question. The refractometer I linked to can (not very accurately) measure TDS in the ballpark for espresso. Not brewing water.

Ciaran

#5: Post by Ciaran »

violin_geek123 wrote:Can anyone recommend a reliable and cheap TDS pen or meter? I'm only looking for a general ppm number for my brew water to check that it's in the ballpark after I make it (currently making batches of Rao/Perger with minerals and distilled water).
The HM Digital COM-80 is about the cheapest decent TDS meter you can buy, which has selectable factors (EC, .5, and .7). On amazon for around $35. Something with adjustable factors, meaning you can change the factor in increments at a resolution of .X, start around $60. Most cheap ($10) TDS meters on Amazon are actually salinity meters for aquariums. They are calibrated specifically for NaCl/Sodium Chloride with a fixed factor of .5. These are generally going to give you a result that is 30% under your actual TDS.

Ciaran

#6: Post by Ciaran »

Factoring is used to correct for the electroconductivity of the underlying analytes you expect to measure. This allows you to have a more accurate and predictable result.

Ciaran

#7: Post by Ciaran »

FYI, you can't use a refractometer to measure TDS in freshwater for brewing. The concentration of minerals is far too low.

violin_geek123

#8: Post by violin_geek123 »

This is all super helpful, thanks everyone!
Brian Hong