Hardness, Total Hardness, Carbonate Hardness, TDS, and so on

[Mike Snaden]

Some of the following is fact, and some of it is my own theory (as far as my calculations at the bottom are concerned). Make of it, what you will...

Water Hardness, Carbonate Hardness, Alkalinity, and TDS.

Following recent debate, I have decided to encapsulate all of the above parameters into an article that will help clear up what each parameter is made up of, and it's function.

GH (General Hardness) is generally accepted as being a measure of Ca++ (Calcium) and Mg++ (Magnesium) ions present in a water sample.


Carbonate Hardness is the level of Carbonate and Bicarbonate buffers in a water sample.

Alkalinity is the quantity of all acid neutralising ions present in water.

TDS, is effectively conductivity, or if you like, Total Dissolved Solids.

GH and KH explained (please note that 17.86 mg/l is used below, as this equates to 1dH)
General Hardness although purely a measure of Ca++ and Mg++ ions, is actually measured as 'GH as CaCO3'. This makes no reference to whether Carbonate Hardness is present or not, but as a figure of how much CaCO3 would be present is these ions were part of Calcium Carbonate. So, remember, if it is referred to as 17.86mg/l CaCO3, this means it would be 17.86 mg/l. IF it were part of CaCO3. The reason for this is simple… In a normal pond pH, the Carbonate level will exist primarily as Bicarbonates (HCO3). As the pH approaches 10.25, the Carbonate level will exist predominantly as Carbonates (CO3). In a lower pH, the Carbonate ions each form Bicarbonate ions.
Since hard water is a result of water often permeating through limestone, much CaCO3 (Calcium Carbonate) will become become dissolved into the water. When this happens, for each 17.86mg/l that becomes dissolved into the water, there will be 7.143mg of Ca present, and 10.714mg of Carbonate ions. So, even though the quantities of each of these components are different, the Ca ions will be measured as “17.86mg/l as CaCO3â€Â

[Mike Snaden]

Well, the above post was extremely long winded, and I have to say, nobody that I have been in contact with has understood the point!

So, tonight, I conducted an experiment...

I took 1 litre of RO water, with a TDS of 5ppm (Residual reading probably due to CO2, O2, etc)

Then, I added some Sodium Bicarbonate. The TDS level had now risen to 363ppm (mg/l).

Then, I tested the KH with an Aquarium Pharmaceuticals KH test kit.

I emailed Duncan and Bob Hart immediately after this experiment, with the following...


Hi guys,

I took 1 litre of RO water (5ppm TDS), and added Sodium Bicarbonate
to it, and got a TDS of 363ppm. How much Carbonate Hardness did I
have as a result?

Mike.

[Mike Snaden]

Here was Duncan's answer, which, I have to say, is EXACTLY what I expected him to say (and scientifically correct), but at the same time... WRONG!

So, here was Dunc's answer...

Quote>

"NHCO3 sodium bicarbonate

1 atom of sodium ( Na)
1 atom of Hydrogen ( H )
1 atom of carbon (C)
3 atoms of Oxygen (O)

Element atomic wt No of atoms/molecule total atomic weight

sodium 22.99 1
22.99
Hydrogen 1.01 1
1.01
Carbon 12.01 1
12.09
oxygen 16.00 3
48.00
total molecule weight
84.00

carbonate CO3

carbon 12 01 1 12.09
oxygen 16 3 48.00
Total 60.09

363 PPM TDS = kh 254 ppm KH


of the total atomic weight added the percentage of carbonated V sodium
bicarbonate is 71.4 % of the total atomic weight = answer 259 ppm KH
minus 5pp to start with 254 ppm KH aprox ( thats give or take for
erroneous measures)"

[Mike Snaden]

Bob's reply...

Quote>

"Yeah you beat me to it Dunc - LOL

Regards, Bob

><{{{{º> ><{{{{º> ><{{{{º>
<º}}}}>< <º}}}}><"

[Mike Snaden]

Well, here is an explanation...

We know, that that by the addition of Sodium Bicarbonate to pure H2O, only the Carbonate Hardness (KH) will be effected, and that the Sodium ions don't contribute to water hardness, and hence, won't show up on a GH test kit. This was confirmed by the GH test being zero.

Anyway, the KH test result was 375ppm (21dGH). you ask, "Why so high!???"... Simple, take a close look at any GH or KH test kit, and it will say that the reading given as CaCO3 (Calcium Carbonate).

What does this mean???... The reading the test kit gave, was "as Calcium Carbonate". This doesn't mean that Calcium Carbonate was present, but simply means that 'IF' the Carbonate WAS part of Calcium Carbonate (CaCO3), then there would be 375ppm (mg/l) of Calcium Carbonate.

So, Duncan based his answer on atomic weights of NaHCO3, which was ABSOLUTELY correct!!!

But, since I knew that the test kit would give the result "as CaCO3", I calculated my atomic weights from CaHCO3 (knowing that the Carbonates would be present as Bicarbonates, and despite the source being NaHCO3), and came up with 252ppm (mg/l).

My point is, that whether you test GH, or KH, the reading WILL ALWAYS be as "mg/l as CaCO3" So, to keep a consistent measurement of either KH or GH, the tes result will 'assume' that the parameter tested WERE CaCO3, not simply a component of CaCO3. So, if you were a person who believed that you could add the KH to the GH, and call it 'Total Hardness', this simply won't add up right. Just imagine that you dissolve 100mg of pure Calcium Carbonate (CaCO3) into pure H2O. In short, you could say that a KH kit would detect the 60mg/l of CO3- ions present, and give a KH result as "100mg/l as CaCO3" despite only 60mg/l of CO3- ions being present, whereas a GH test kit would give a result of "100mg/l as CaCO3", despite only 60mg of CO3 (Carbonate) being present. If you then added the test kit's 'point of reference' readings together, you would get a reading of 200mg/l. which we all know just isn't true, since only 100mg/l of Calcium Carbonate was added in the first place!
So, laboratories need to be able to quantify things as a measurement. Either KH or GH, will be measured as 'mg/l as CACO3', even if only Ca ions are being tested, or only CO3 ions are being tested.
Does it all make sense now?

Goodnight for now...

Mike.

[Bob Hart]

Mike,

My answer was very flippant and I apologise.

I saw your question after consuming some 'Red' and though 'blimey' or words to that affect. Duncan's reply was already on my PC by then and seeing that made me also think 'blimey', or similar words. Atomic weights of various elements are certainly not my speciality, in fact I'll go so far as to say I haven't the faintest about them and would have no reference points. I'm only posting this because I think 99% of us common Koi keepers will be thinking the same.

Now with a clear head and if I'd just received your question, I'll answer it as I would have from a common Koi keepers angle.

5ppm residual TDS
Sodium Bicarbonate then added
TDS now 363ppm
What would the KH now be?
I would have said that as Sodium Bicarbonate is added to increase the KH and therefore stabilise the pH in a Koi Pond, that the KH would have been 363 minus 5 = 358.
This answer would have been based purely on the above and without any scientific analysis.

I'm guessing that most of us would have answered similarly.

[Gazza]

Well i am still reading the question

[Duncan]

Bob / Gazza

to tell Truth i was the wrong side of a bottle of malt when that landed too, im surprised i got it right< grin>

in all honesty its not something you really need top know, its nice to know, but not essential to know at all unless it presses your buttons, you just use your test kit as you have always done the fact that it measures as though calcium were present makes no difference to you or me its just number crunching and the calcium adds nothing to the KH buffering efficiency at all, in fact CaCo3 or CaHCo3 is a pretty lousy buffer for our purposes as fish keepers anyway

below is some slides of how i worked it out for those that want to know
i have done it in slide type presentation so you can see the layout as everything gets squashed up in type and then makes no sense
so if your interested here it is if you now dont go here

but as this thread is getting some serious hits i thought it prudent not to leave it to speculation

Duncan
[img]http://koiquest.co.uk/bicarb1.gif[/img]

[img]http://koiquest.co.uk/bicarb2.gif[/img]

[img]http://koiquest.co.uk/bicarb1.jpg[/img]
you can see from he above the Bicarb ions has three oxygens attached to one Carbon and one of those oxygens has a solitary hydrogen attached to it

[img]http://koiquest.co.uk/carbonate.gif[/img]

the above is carbonate ion which is essentially the same but with no additional hydrogen atom as you can see the bicarb molecule has not go two more of anything that the carbonate has not got except the hydrogen

the periodic for carbon is big C and the ate on the end of carbonate simple means it has extra Oxygen to whats normal indicated by the periodic assay of O3 ( 3x oxygen)

[co2]

Oh bob
I wish you had pointed me in the Wright direction, I thought you meant previous articles by mike.

This makes things a lot clearer (yeah as mud)
Just when I thought I was getting an elementary understanding of water chemistry you come out with this mike.
So what does this mean for the humble tds meter?
Does it depend if you have a pessimistic or optimistic view of the readings?
And how does one utilize this information if the input water is too soft to run the pond un buffered. And trying to follow low tds in the form of dissolved organics.
John

[Bob Hart]

Bit of a handfull this John!

[Gazza]

Or what about conductivity is this better than TDS

What about the TDS meters that are used for different stuff as some will have a conversion factor of 0.7 and some 0.5

Still i think we do sometimes go a little over the top

[co2]

Conductivity meters. Conversion factors. 0.7 0.5
Oh my head really hurts I’m filling in the pond and building a golf course.
John.

[Gazza]

Its all just stuff John

[co2]

Agreed gazza
But it seems I am finding out the hard way its not all about filtration.
If your water chemistry isn’t right it doest mater how much or how good your filtration is. It just wont cut it.
Boo hoo.
john

[Gazza]

Well water is the most important thing look how much we have around us and how little we know about it