Conductivity or TDS

[farm41]

Which one should I monitor? Conductivity or TDS

I would like to buy one of these meters, but I don't know which one to get. Does it make any difference?

 

[aspen]

discus breeders find that good egg fertilisation is related to conductivity. i would suspect that it is the same for breeding apistos and tetras, as well as other s/a fish.

rick

 

[Randall]

Measuring Conductivity

Dear Farm,

I think Rick makes a very good point. When breeding soft water fish, sometimes conductivity that is too high can prevent the eggs from being fertilized and/or they simply don't develop properly. The same problem can be caused by alkalinity levels that are too high.

I use a conductivity monitor because both some of the better popular literature as well as scientific descriptions commonly cite conductivity levels measured in microsiemens. With the meter, one can better approximate the water chemistry that the fish would experience in their natural habitat. I've found that this is especially valuable when breeding wild fish.

Good luck.

Randall Kohn

 

[farm41]

Thanks Rick and Randall.

Does any manufacture one that can be connected to a DMM? I have a Fluke 83, it would be nice to find something that could work with it.

 

[mordor]

I got Hanna pH/TDS/conductivity meter and you can either calibrate TDS or conductivity. Other value will be derived from calibrated value so I guess they are depenendent to each other.

 

[Scooter]

If I'm not mistaken, there is a conversion for microSiemens/cm to TDS at a given temperature. I don't know what that ratio is, but I'm pretty sure one exists. If that's the case, I would imagine either type of tester would work. Of course you would have to do the conversion yourself, which would probably be tedious until you've memorized the conversion rate

 

[farm41]

I would really rather buy the one that I don't need to convert for. Haven't ordered anything yet.

 

[Scooter]

I don't blame you, but thought I'd throw that out as an option. I think those all-in-one testers are a little pricier. I use a TDS tester and am quite satisfied.

 

[Mike Chappell]

Hey guys...Just wanted to drop a line...in case ya don't know me, I am owner of Three Guys Aquatics, an authrorized retailer for Hanna Instruments. TDS and Conductivity are dependent on almost a 2:1 conversion from TDS- Microsemions. And temperature does play a factor, but not a signifigant one. You will see meters, really if the meters are equal accuracy, they will be closely priced. Most of the time the conductivity pens are higher accuracy, therefor more pricier. TDS pens are quite cheap if your just looking to get an idea of your water parameters. Both can be calibrated with a control solution. The all-in-one meters are more pricier as mentioned, sometimes you end up paying for specs that you didn't need. I find it most feel seperate meters for what they want is best. Just my feedbacks. Hope this helps.

Mike Chappell
Three Guys Aquatics

 

[tjudy]

TDS can be affected by solutes that are not conductive. That is one reason to have a meter that can measure both.

As far as price on meters goes, it all depends upon how many meters you want to buy. Hanna Instruments produces a Combo Meter that measures pH/EC/TDS/temp. It automatically adjusts for temperature differences as well. Four meters will cost you more than just one...

Anyone interested will soon be able to purchase Hanna meters through this site. They will be listed in the fishroom's misc. products page within a couple weeks. If you are in a hurry, feel free to e-mail me.

 

[Mike Chappell]

Hey there,

I am interested in factors that can be measured by tds or affect readings that would make these two differ? I would be interested to learn of the solids that would not be picked up or would be picked up that a conductivity meter wouldn't/would. I am very familiar with sciences, please explain if you would. I am intersted on learning this....

Price involves a few factors also, # of parameters being measured is one, and also accuracy of those readings makes the difference even more so. Lab grade equipment can be quite pricey compared to what we need/use.

Thanks..

 

[tjudy]

My understanding is that carbonate hardness (kH) is not as conductive as other solutes such a chloride salts; and that a TDS meter will measure a combination of the two, while a conductivity meter will not.

Mike, I thought Three Guys Aquatics distributed Hanna Instruments? What is your take on their Combo meters vs. their single parameter meters? The TGA site offers the single parameter meters in the $30 - $50 range. A combo meter has a suggested retail of about $150, and measures pH/TDS/EC/Temp.

Anyone interested in seeing the details can go look at www.hannainst.com. They provide a lot of information about their meters.

 

[aspen]

ted, is this the meter which you are referring to?

http://www.hannainst.com/products/testers/combo.htm

it comes with a ph probe. does this mean that different probes need to be used for different readings? (ec, tds and temp) do they need to be swapped out, to get that other reading?

rick

 

[tjudy]

That is the meter I am looking at Rick. My understanding is that the meter does not need to have probes exchanged. The pH probe described on the sheet is to show that the probe can be easily replaced. I also checked with Hanna and the suggested retail price of those combo meters is $130, not $150.

I have some clarification on the EC vs. TDS issue. I surveyed two chemical engineers, a former chem professor and two chem teachers (all of them are actually teachers), and the answer was unanimous: EC does not measure the pressence of insoluble substances like calcium carbonate. That means that EC does not accurately measure hardness in water with carbonates in it. Most carbonates are either insoluble or only dissolve slightly.

EC measures the levels of dissolved ions, which conduct electricity. TDS will measure the presence of both soluble and insoluble substances; which I have always referred to as TOTAL HARDNESS. The hardness caused by carbonates is what I have always been told is CARBONATE HARDNESS (or kH), and is a measurement of a solutions buffering capacity against pH drops.

:?
I have always been confused by the German system; so PLEASE correct me if I am wrong:
kH - carbonate hardness - read by a TDS meter, not by an EC meter
dH - degrees(?) hardness - read by an EC meter and TDS meter
tH - total hardness - combination of kH an dH - measured by TDS meter
:?

:?:
Does this mean that kH can be estimated by comparing a TDS reading to an EC reading? If TDS is high, but EC is low, does that mean that the hardness is due to insoluble carbonates?

 

[aspen]

ok! this is good. i want to get this straight too.

imo, gh, is 'general hardness', and is a measure of the things in water which mke it hard, ie, inhibit soap to foam. and these are, magnesium and calcium ions only. in fact most gh kits spec say, general hardness is a measure of calcium and magnesium and this is what is tested for. is there any other 'hardness' materials other than ions of these 2?

kh, means carbonate hardness, BUT, the test kits all say that alkalinity and carbonate hardness can be used interchangably. they are different though. many substances can contribute to alkalinity, and are not carbonates and bicarbonates, ie phosphates. all kh kits i have seen spec say, they measure alkalinity, but they usually use these 2 words interchangably.

>>'...a measurement of a solutions buffering capacity against pH drops.' i believe that this is alkalinity, not carbonate hardness, although in most water samples kh is the mayor component. the reason this is important, is when measuring the effect of acids (like co2 f/i) will have on a sample where other than carbonates are buffering the water's ph (like phosphate buffers). but if you are using a kh kit, then you are measuring the total alkalinity, not kh only.

there are supposed to be a way to measure 'carbonate hardness', but i am not sure how this is done.

ec= electrical conductiity, and is a measure of how well the water conducts electricity. simple right? that means that only the metal ions (like magnesium, sodium and phosphorous etc) are being measured as a part of this.

tds = total dissolved solids, and measures EVERYTHING. how does it work, or, how can a meter measure things that won't increase the conductiity or water? i don't know about that one. weight of the water is the only way that i can think of, and i know a tds meter doesn't do that.

calcium carbonate doesn't dissolve in water? i'm not sure about that. i thought that it was dissolved, until the water is heated and then becomes scale . (say on the bottom of your kettle.) carbonates are easily brought out of solution and are therefore often called 'temporary hardness', as opposed to 'permanent hardness'.

dH is degees of hardness, and is interchangable with gh, afaik.

rick

 

[tjudy]

Calcium carbonate does NOT break apart in water... like salts do. That is why it is not considered 'soluble'. Technically, sugar is not soluble either, because the sucrose molecule does not fall apart. What we see when we put carbonates in the water is the molecules separate from each other and disperse. They do not break into ions, and therefore are not conductive.

 

[Neil]

So, does anyone actually have one of these multipurpose units that can give us some feedback on how well they work. I am personally very interested in economizing my equipment and would love something that I can test everything including temp, with one unit!
Neil

 

[tjudy]

I will have one by the end of next week... I want to give it a test run.

 

[farm41]

That's great Ted, I still have not ordered mine yet.

 

[farm41]

There was a discussion over at simply discus that raises the question.

http://www.simplydiscus.com/forum/index.php?board=1;action=display;threadid=287

Are conductivity and TDS meters that hobbyist use measuring just EC and converting the numbers for TDS? Or, are they really measuring what they are supposed to?