# TDS Meter recommendations?



## SpaceBug (Jan 10, 2007)

I'm going to order a TDS meter for checking the output of my RO unit. Are they all pretty much the same? Any personal experience that you could relate will be appreciated.


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## Laith (Sep 4, 2004)

If you're going to spend the money on a TDS unit, it may be an idea to check this unit out:

HI 98129: Combo

For a bit more money you also get a pH meter and temp.  Of course this assumes you want a pH and temp meter!


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## t2000kw (Jul 29, 2006)

I got a TDS and temp meter for less than $25 on ebay. Shipping was free because I had it shipped with my RO unit when I purchased it.

Works well. It also is useful to tell you if solids are building up in a tank over time so you know to change the water, even if chemical tests are all OK.


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## diablocanine (Jul 25, 2004)

I have this kind, works fine and is $17 shipped....DC
eBay: HANNA TDS1 TDS PPM Tester/Meter, Ionic/Colloidal Silver (item 280082683807 end time Feb-21-07 06:17:21 PST)


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## SpaceBug (Jan 10, 2007)

Good to see a couple of recommendations for the Hanna testers. I have a pH monitor/controller where the probe is in the filter return line. So I've been eyeing the Hanna combo probes so I could have a TDS tester and another pH tester to check on my in-line probe.


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## Salt (Apr 5, 2005)

I personally recommend American Marine products. I have found that they give the same performance as high end lab products for much less.

Of course they are not the company do go with if you don't care about quality and only want the absolute cheapest product you can get.


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## diablocanine (Jul 25, 2004)

Salt said:


> I personally recommend American Marine products. I have found that they give the same performance as high end lab products for much less.
> 
> Of course they are not the company do go with if you don't care about quality and only want the absolute cheapest product you can get.


I thought spacebug was asking for a TDS Meter recommendation. Does American Marine make a TDS meter? I could not find one with the link provided.....DC


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## Laith (Sep 4, 2004)

I've never used the American Marine products but have heard good things about them. I think their "Pinpoint Conductivity Monitor" is for TDS.

I've never had an issue with Hanna Instruments and, at least over here, they are not cheap. The Combo pH/TDS/temp meter I linked to sells for around €150 plus shipping (about US$185). Their basic pH meter sells for around US$125. The DiST 5HI TDS monitor goes for US$ 143.

But Salt makes an excellent point: most of the time buying the cheapest ends up costing you more in the long run!  Get quality stuff from the beginning, even if you have to wait a bit.


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## yxberia (Apr 19, 2005)

You can try company selling water filtration system, RO Unit parts. They can get you a basic TDS pen-tester with very low price. Hanna (old model) works for me and very cheap too.


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## Salt (Apr 5, 2005)

diablocanine said:


> I thought spacebug was asking for a TDS Meter recommendation. Does American Marine make a TDS meter? I could not find one with the link provided.....DC


They make two models. They just don't call them "TDS meters." I didn't link them because it breaks the frames on their website.

The first one is for measuring lower concentrations of dissolved solids, mainly for freshwater tanks. It's the "Conductivity Monitor."

The second is for measuring higher concentrations of dissolved solids, mainly for seawater tanks. It's the "Salinity Monitor."


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## diablocanine (Jul 25, 2004)

Salt said:


> They make two models. They just don't call them "TDS meters." I didn't link them because it breaks the frames on their website.
> 
> The first one is for measuring lower concentrations of dissolved solids, mainly for freshwater tanks. It's the "Conductivity Monitor."
> 
> The second is for measuring higher concentrations of dissolved solids, mainly for seawater tanks. It's the "Salinity Monitor."


I'm sure that explanation was appreciated for the novices to TDS, I doubt most would have known that from the link.

"Of course they are not the company do go with if you don't care about quality and only want the absolute cheapest product you can get."

If you are refering to hanna, that is a very inaccurate statement. I have used and know plenty of folks that have hanna equipment with no issues. Cost is not always an indicator of quality and/or proof of purpose......DC


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## OldManShiver (Mar 30, 2004)

Just curious as to why anyone would spend the extra on a conductivity monitor when TDS meters can be had so much cheaper? They tell you same thing, no?


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## banderbe (Nov 17, 2005)

I use a Hanna Primo 1 TDS meter. Easy to calibrate, and works flawlessly. Additionally it automatically adjusts for water temperature.


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## Laith (Sep 4, 2004)

Graham said:


> Just curious as to why anyone would spend the extra on a conductivity monitor when TDS meters can be had so much cheaper? They tell you same thing, no?


A TDS meter *is *a conductivity meter... it calculates ppm TDS by measuring the conductivity. Some meters convert the reading into ppm TDS and display that, others display in mS/cm (microsiemens per centimeter).

All you ever wanted to know about TDS/conductivity meters:

http://www.reefkeeping.com/issues/2004-04/rhf/feature/index.php


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## banderbe (Nov 17, 2005)

Laith said:


> A TDS meter *is *a conductivity meter... it calculates ppm TDS by measuring the conductivity. Some meters convert the reading into ppm TDS and display that, others display in mS/cm (microsiemens per centimeter).
> 
> All you ever wanted to know about TDS/conductivity meters:
> 
> http://www.reefkeeping.com/issues/2004-04/rhf/feature/index.php


It's probably a many to one relationship- a range of conductivity readings convert to the same TDS value.

I have a $400 conductivity meter and while my Hanna Primo 1 TDS meter shows my RO water to have a TDS of 0, the conductivity meter (if I remember correctly here) showed 0 TDS water to have a conductivity of 20 microsemens or something like that.

But you can have ultra-pure water used in semiconductor fabrication that has a conductivity of 0, which of course is also TDS 0.


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## OldManShiver (Mar 30, 2004)

Laith said:


> A TDS meter *is *a conductivity meter...


I guess that's what I was inferring. When someone could have a TDS meter for $25 while conductivity meters run at least $100+... what's the point?

But one thing I have noticed is that the reputed equivalent equations for TDS and GH don't jive for me. I have a tank that measured something like 170 ppm TDS and the GH was only 6. The GH kit is fairly new and the TDS meter is calibrated using distilled water and a TDS standard (1382 ppm or something). Since I assume that GH is really only measuring Ca and Mg (no?), and there are more solids than that in the tank, why do the supposed "equivalents" between TDS, conductivity and GH even exist?

What am I missing?


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## t2000kw (Jul 29, 2006)

TDS meter technology is cheap, so any low cost one will probably work well for a long time. Test it on distilled water or RO/DI water and if it reads low (like 2-5) it is probably just fine. RO (without a DI filter) water should read higher, mine is around 22-24. I followed a link from a post (see below) and it's interesting that TDS meters use different methods of arriving at a number. Numbers will be different between brands that use different methods, too. But in any case it's a relative reading you are looking for anyway, so the method used doesn't really matter.

http://www.reefkeeping.com/issues/2004-04/rhf/feature/index.php

Conductivity meters are actually more "accurate" since they don't convert to TDS in ppm. So the conversion error is avoided. But I prefer the simplicity of a TDS meter since I'm not working in a lab.

On the other hand, a pH meter uses more expensive technology and the tip is where the quality is. If you get a combo unit, it may pay to buy a quality meter. You want to keep the tip moist and protected with the included cap/tip cover.

If your only concern is TDS readings, you may find a cheap one serves you well. You may find it better to buy a cheap TDS meter and a good pH meter. You won't have to pay it all out at once that way, and if one of the meters quits on you, you don't have to replace a much more expensive combo unit. The overall cost may be less as well. I prefer to not have everything tied together in electronic appliances. Sometimes it IS cheaper, but if one part breaks, it often leaves you with a larger payout to replace it than if only one separate component needed replaced.

That said, many people do like the TDS/pH meter combo units, and it's your money, so you have to decide the best way to go.


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## OldManShiver (Mar 30, 2004)

I have both (pH and TDS). My confusion lies in the puported "equivalents" between TDS/conductivity/hardness.

So if....

TDS:
_"Total dissolved solids (TDS) is a measurement of the total amount of dissolved substances in water and expressed in ppm of NaCl. TDS is essentially the same as conductivity."_

Regarding GH:
_"Water hardness is the measurement of the amount of ions which have lost two electrons (divalent cations) dissolved in the tested water and is therefore, related to total dissolved solids. The more divalent cations dissolved in the water the "harder" the water. Generally the most common divalent cations are calcium and magnesium, however other divalent cations may contribute including iron, strontium, aluminum, and manganese."_

Conductivity:
_"Conductivity or specific conductance is the measure of the water's ability to conduct an electric current. Conductivity depends upon the number of ions or charged particles in the water."_

How can there be any equation among three parameters that measure 3 different groups?
I see things like "uS = TDS x 0.64", when this is really not a proper correlation. Maybe "close enough", but not equal. The amount of conductivity may partially depend on the concentration of Na and Cl in the water, but there are likely more ions contributing to conductivity than that. Likewise, if my TDS meter is calibrated to an NaCl standard, how would I expect it to accurately measure (or even detect) anything else? I'm not too worried about there being any Na or Cl in my RO/DI, but I would be concerned about NO3 or PO4...or heavy metals.


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## OldManShiver (Mar 30, 2004)

All that said, I think conductivity may actually be the far better parameter to measure. It will detect far more "non-water" components in the water. I guess I've reasoned myself into the significance of the parameter after my initial naysaying. I'm still not quite to the point of dropping the cash on a meter, but I'm sure it's only a matter of time...


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