Should Neptune's 2 TDS water worry me?

[JVU]

The inexpensive inline ones from HM Digital that everyone uses in their RODI unit are good and reliably measure the differences we want to know. No reason to go crazy here. 0 TDS is easily achievable with basic care and maintenance of an RODI system. If you don’t keep up with basic care and maintenance your TDS will creep up, which signals that it’s time to do maintenance again.

And to be clear, I trust Robert and Neptune Aquatics, so in that particular and specific case I would trust their water is safe when they say it is. But otherwise in general I’m not satisfied with unknown contaminants in my water. You can have successful tanks without worrying about TDS as others have said, but unlike lots of other things in the hobby it is trivially easy to just get it right so why not.

 

[NanoCrazed]

On Amazon there's a billion of them for $10-$20. I bought a couple, tested a couple samples, and then returned all but the one that seemed accurate. My testing samples were some RO, some RODI, some distilled, tap, and some RODI with varying bits of salt in it.

I was just looking for one that consistently reported 0 for the distilled water, and oversee increased when I threw some salt in the water. I figured all the really matters is it registers 0 when it should, and non zero when it should. Knowing if it's 2 vs 3 TDS seemed to me not super actionable. I'll just use it to change filters when I see it creep up, along with seeing if my DI resin changed color.

And fwiw, the super expensive one I bought, thinking it'd be the most precise, was one of the least informative ones. It only measured in increments of 5. I ended up keeping one that cost about $12 and came with a pH meter too (though I never tried to pH meter and online reports they're garbage).

Edit: I also debated if it was moral to buy multiple knowing I'd only keep one. I normally wouldn't do that, but here if they're not giving me a correct number they're literally not working properly, so it seemed appropriate.

BTW -- many of the TDS meters can be calibrated. So, can easily get to a zero baseline for distilled if needed.

 

[richiev]

BTW -- many of the TDS meters can be calibrated. So, can easily get to a zero baseline for distilled if needed.

I don't think the super cheap ones can be calibrated. At least, outside of the expensive one I got, none of them were calibratable. The pH meters in theory were, but I didn't do that.

 

[richiev]

The inexpensive inline ones from HM Digital that everyone uses in their RODI unit are good and reliably measure the differences we want to know. No reason to go crazy here. 0 TDS is easily achievable with basic care and maintenance of an RODI system. If you don’t keep up with basic care and maintenance your TDS will creep up, which signals that it’s time to do maintenance again.

And to be clear, I trust Robert and Neptune Aquatics, so in that particular and specific case I would trust their water is safe when they say it is. But otherwise in general I’m not satisfied with unknown contaminants in my water. You can have successful tanks without worrying about TDS as others have said, but unlike lots of other things in the hobby it is trivially easy to just get it right so why not.

Fwiw, I included a HM digital inline meter in my test, and at least the one I got didn't give good readings. I believe it was giving me 2 TDS even on distilled, and was reading 40 on liquids other things were agreeing were around 30.

I imagine all these have very low quality control, given the price. It's likely worthwhile to test any of them against a reference, and buy from a provider with easy returns.

 

[Devon]

On Amazon there's a billion of them for $10-$20. I bought a couple, tested a couple samples, and then returned all but the one that seemed accurate. My testing samples were some RO, some RODI, some distilled, tap, and some RODI with varying bits of salt in it.

I was just looking for one that consistently reported 0 for the distilled water, and oversee increased when I threw some salt in the water. I figured all the really matters is it registers 0 when it should, and non zero when it should. Knowing if it's 2 vs 3 TDS seemed to me not super actionable. I'll just use it to change filters when I see it creep up, along with seeing if my DI resin changed color.

And fwiw, the super expensive one I bought, thinking it'd be the most precise, was one of the least informative ones. It only measured in increments of 5. I ended up keeping one that cost about $12 and came with a pH meter too (though I never tried to pH meter and online reports they're garbage).

Edit: I also debated if it was moral to buy multiple knowing I'd only keep one. I normally wouldn't do that, but here if they're not giving me a correct number they're literally not working properly, so it seemed appropriate.

Awesome information! Do you have a link to the one that you have had success with?

 

[richiev]

tl;dr: I'd buy with the intention to return if the numbers look wonky. These are just so cheap there's no way they're being tested properly before sales

Info on ones I tested, purely based on memory:

* GroTheory TDS: this is the one I kept. It gave me 0s on distilled & RODI, 30ish on my tap which was aligned with the other ones I tested, and if I tossed some salt in the distilled I could see the reading go up.
* HM Digital DM-1: I like the form factor, great to be able to plumb inline, was giving me slightly off readings (eg distilled = 2TDS)
* Bluelab $343 monitor: Super expensive, I didn't have any real justification for spending it, but I thought it might be the gold standard and I might as well test it. Only was giving readings with 5 TDS intervals (eg 0, 5, 10, 15, ...). Was within aligned with the others. I think it came with calibration fluid, but I figured the odds of me keeping it was low and didn't want to abuse things so I didn't use it. Also it might have just had PH calibration fluid, I can't remember. It's probably fairer for this thing to be using less granular data, and I imagine the other ones aren't actually as precise as they imply, but I can't see why you'd pay that much for something that wouldn't give you some signal between 0 and 5.
* VIVOSUN pH and TDS combo: I can't remember if this was accurate or not. I think this one said distilled = 2 TDS, but I'm not sure. I never tested the pH
* PH and TDS: I can't remember if this was accurate or not. I think this one was accurate, but I actually ordered this one on accident so I returned it. I never tested the pH

If you look at the form factor on most of those, they're almost identical. Even the colors are the same. My assumption is they're all just the exact same units, some of which someone printed a name on to it (eg VIVOSUN). They all looked and worked exactly the same.

So my assumption is it's all a crapshoot and just buy one, test it on distilled, then distilled with some salt in it, and see what you get. If you get distilled reads 0, crap in it reads non-zero, consider that one good. I personally would prefer to have the inline ones (the HM Digital), so at some point I might reorder one of those and give it another try. I personally would also just buy the cheap ones, based on what I saw and how infrequently I'd expect to look at that data.

 

[rygh]

Really two options:
1) Buy a cheap probe, and stop chasing numbers.
That 2 TDS in your RODI water is below the range cheap meters can really measure properly.
Some people actually run reef tanks with tap water. (Neutralize chlorine, then just add a but less Salt/Alk/Ca when mixing to make it come out right.)

2) Get fancy.
And key to that is the PROBE. The electronics are pretty easy.
You need a very low K probe so that you can measure in the range needed for pure water.
https://atlas-scientific.com/probes/conductivity-probe-k-0-1/

 

[Flagg37]

Really two options:
1) Buy a cheap probe, and stop chasing numbers.
That 2 TDS in your RODI water is below the range cheap meters can really measure properly.
Some people actually run reef tanks with tap water. (Neutralize chlorine, then just add a but less Salt/Alk/Ca when mixing to make it come out right.)

2) Get fancy.
And key to that is the PROBE. The electronics are pretty easy.
You need a very low K probe so that you can measure in the range needed for pure water.
https://atlas-scientific.com/probes/conductivity-probe-k-0-1/

So are TDS meters and conductivity probes the same thing just giving different units of measurement?

 

[rygh]

So are TDS meters and conductivity probes the same thing just giving different units of measurement?

Yep.
TDS and also the electronic Salinity probes measure Conductivity and convert.

Technically they are different things. The real way to measure TDS is to evaporate all the water, and weigh what is left.
But conductivity is close enough.

 

[rygh]

So are TDS meters and conductivity probes the same thing just giving different units of measurement?

If you are curious:
What they really do is apply a carefully controlled AC voltage on two plates, and measure the current.
Given distance between plates, size of plates, and minimal metal interaction, you can calculate all 3 things.
That last part is why a quality probe is important.

 

[Meshmez]

Fwiw, my understanding is the HM digital DM-1 NEEDS to be plumbed in line and have water running past it. Using it in still water would not yield proper results. I also believe they need to be installed in the tube so they are oriented so that water runs through the middle of the pins, not around them (perpendicular to flow, not parallel)