TDS Meter Question

[inetmug]

Hi all,

I recently got a TDS meter from autotopoff. The unit is self calibrating per the instructions. I get a reading of 002 in distilled from a local supermarket, I get around 300 on the tap, which is believable for sure.

I would have thought the TDS would certainly been zero with distilled. To be sure, I want to check something. The three numbers on the screen, represent 10ths, 100th, 1000th? I have read that even distilled really does not have a "zero" reading of PPM. But I have no idea really. So either this meter is honked, or maybe very good?

So for for my reading in distilled, that is 2000ths of a PPM, and or a reading of "2"? Many RODI manufactures I have seen recommend changing filters at "5", so this would be 005 on the meter?

[disc1]

Hi all,

I recently got a TDS meter from autotopoff. The unit is self calibrating per the instructions. I get a reading of 002 in distilled from a local supermarket, I get around 300 on the tap, which is believable for sure.

I would have thought the TDS would certainly been zero with distilled. To be sure, I want to check something. The three numbers on the screen, represent 10ths, 100th, 1000th? I have read that even distilled really does not have a "zero" reading of PPM. But I have no idea really. So either this meter is honked, or maybe very good?

So for for my reading in distilled, that is 2000ths of a PPM, and or a reading of "2"? Many RODI manufactures I have seen recommend changing filters at "5", so this would be 005 on the meter?


The reading on your TDS meter should be in ppm not in ppb. Where are you seeing that those numbers should be tenths and hundredths of a ppm?

It's not uncommon to register some TDS on ultrapure water. As soon as you open it to the atmosphere it pulls in gasses from the air like CO2 that will register as TDS.

[disc1]

Can you link to the meter you have?

[inetmug]

Can you link to the meter you have?

http://autotopoff.com/RO/

Need to move down the page.

Regarding the numbers, I was wondering how to exactly interpret it. So the meter can read from 0 to 999 PPM period.

I see so many people that read 0 TDS off their RODI, I read 002 off my distilled...

[disc1]

Well that got me to a picture of it but not really to any details. However I'm fairly certain that any TDS meter you buy for 11 bucks doesn't read out less than one ppm. So you may be mistaken about the tenths and hundredths and thousandths. I think it is just reading in ppm. Getting TDS sub-ppm level is usually going to cost you a good bit of money.

In my reply above I gave you the reason why you're reading higher. Most of it is dissolved gasses and part may be from the bottle it was in. Either way it's not something to be concerned with.

[inetmug]

opened a brand new bottle of distilled, took a clean plastic cup, rinsed it, and presto a reading of 000. An hour later, some kaka in the cup, and 001. Thanks bud!

Probably not the best meter, but my first meter. Accuracy probably not the best.

[Randy Holmes-Farley]

The rise to 1 ppm TDS might be from CO2 entering it from the air (or just random noise). But CO2 will do that. :)

FWIW, the "TDS" of totally pure water is about 0.029 ppm TDS. The definition breaks down a bit since TDS stands for total dissolved solids and no dissolved solids gets a nonzero value due to the inherent conductivity of water. There are also several competing definitions of TDS since it doesn't really say what is dissolved. There are different scales for KCl, NaCl, and something called 442 which is designed to look like some types of river water.

That's why most scientists do not use the unit at all. They use conductivity (mS/cm, or uS/cm) or resistance (such as 18 MOhms for pure water).

Any value you read from a TDS meter that does not show a decimal place is in ppm and not ppb. :)

This has more:

What is TDS?
http://www.reefkeeping.com/issues/2004-04/rhf/feature/index.htm