# Can rock raise GH without raising TDS?



## Lindy (11 Sep 2013)

I have some ADA sado-akadama rock in my 30cm cube. As I keep shrimp I maintain water parameters at GH5 TDS180 but checked the GH in the cube and it is at 8. I had asked the green machine if the rock would change the hardness of the water, before I bought it, and they said it was inert and wouldn't change anything.
I did a water change that brought the gh down to 6 a few days ago but today it is 8 again. TDS always stays the same at 180.


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## Tim Harrison (11 Sep 2013)

I doughnut think so...Raising gh without raising tds | UK Aquatic Plant Society Maybe your test kit isn't very sensitive or a bit faulty...


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## Lindy (11 Sep 2013)

I would have thought it was faulty if it was not giving the usual results for the other tank that doesn't have the rock in it. Weird.


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## Tim Harrison (11 Sep 2013)

Unless...do you use purigen, if so have you recently recharged it, or added fresh carbon? Could it be possible that organic substances have been gradually filtered out of the tank whilst calcium and/or magnesium have risen, to the degree that TDS remains fairly stable but GH increases? Or is that train of thought fundamentally flawed in many different ways that haven't occurred to me...I've been feeling particularly blond recently...


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## dw1305 (11 Sep 2013)

Hi all,


Troi said:


> I doughnut think so..


 Troi is right, calcium or magnesium ions are a component of both GH and TDS, but it really depends on what the GH test is measuring. 





Troi said:


> Unless...do you use purigen, if so have you recently recharged it, or added fresh carbon? Could it be possible that organic substances have been gradually filtered out of the tank whilst calcium and/or magnesium have risen, to the degree that TDS remains fairly stable but GH increases? Or is that train of thought fundamentally flawed in many different ways that haven't occurred to me...I've been feeling particularly blond recently...


 You are having a blond moment, but only because TDS meters measure conductivity, if they really measured TDS the non-ionic compounds would count.

Another possibility is that the organic compounds that purigen removed may have acted as chelators, and bound some of cations.

You get this effect with citric acid, explained here by "Regani" <700 liter Amazone | Apistogramma.com>. 

cheers Darrel


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## Tim Harrison (11 Sep 2013)

dw1305 said:


> Hi all,
> Another possibility is that the organic compounds that purigen removed may have acted as chelators, and bound some of cations.l


 
Yep...that's exactly what I meant...init


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## Lindy (11 Sep 2013)

I don't use purigen.


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## Tim Harrison (11 Sep 2013)

ldcgroomer said:


> I don't use purigen.


 
OK that's that spurious theory out the window, nevertheless...



dw1305 said:


> You are having a blond moment, but only because TDS meters measure conductivity, if they really measured TDS the non-ionic compounds would count.


 
Darrel help me out here I'm a bit confused now...TDS meters measure conductivity so they only measure ionic compounds; those with a net positive or negative charge, right? Purigen removes nitrogenous organic waste which I thought included ionic compounds like ammonia. Both magnesium and calcium are also ionic but supposedly not absorbed by purigen. Therefore, wouldn't it be theoretically possible for the TDS to remain the same if ionic nitrogenous compounds were absorbed by purigen at the same relative rate that magnesium and calcium ions entered in to solution. And ergo for the GH to rise whilst the TDS stayed the same...Chemistry was never my strong point.

I'm not sure exactly how purigen works but it seems that a lot of people experience a stable reduction in TDS when they use it. So despite it's marketing, it undoubtedly has some ion exchange capacity along with its self-professed extreme affinity for nitrogenous organics. But if I've got the above wrapped round my neck this is completely besides the point.


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## Tim Harrison (11 Sep 2013)

I meant ammonium not ammonia...as in ammonium ions excreted directly in to the water by fish and shrimp etc.


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## ceg4048 (12 Sep 2013)

TGS means Total Dissolved Solids. It does not mean conductivity.

There is a relationship but they are not the same. Compounds do not have to be ionic or to disassociate in order to have an electrical effect. They can be dipoles, and this polarization will have an impact. Resins which adsorb un-ionized compounds will do so via the mechanism of Van der Waals forces, which is an intermolecular mechanism and which does not require ionized targets. Also, just because an ion has a charge, it does not automatically mean that it will be adsorbed by the resin. All resins as well as activated carbon target specific molecules based on the relative shapes of the charge fields.

Cheers,


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## Lindy (12 Sep 2013)

Um, Clive, is that a yes or a no?


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## Tim Harrison (12 Sep 2013)

Ahh...intermolecular forces and good old Van der Waals - is all coming back to me now...so that's a yes then - it is theorectically possible...and is it also why purigen can be recharged?...hmmm - _strokes chin in a considered manner_...


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## ceg4048 (12 Sep 2013)

Hmmm...I can see immediately that we need to delve into our remedial chemistry.

OK look, can you see the little bunny rabbit below?
This is a schematic of a water molecule.
The little green ears on top are each a Hydrogen atom with a positive charge at the center of each green ball.
Where the green touches the big purple ball (Oxygen) the Hydrogen, which already has only a single electron (-)
seeks a second electron, but no more than one extra. The purple ball has a total of 8 orbiting electrons, so it can easily share two of them. One spare for each green ball. Each of the green balls now have 2 electrons (one, it's own and the second from one of the 8 that the purple owns). Those electrons zip around, but spends most of their time at that interface where green meets purple. The other electrons owned by the purple are also zipping around but mostly spend their time down at the bottom part of the purple ball. The result is that the bottom of this structure has a strong negative charge but up at the top, where there are much fewer electrons, and where the protons (+) at the center of the green balls are exposed causes that general area to have a positive (+) charge. So because of that the green ears will be attracted to negatively charged particles while at the same time the bottom part of the structure will be attracted to positively charged particles. This is called a dipole and it's almost exactly the same as those little refrigerator magnets that we used to play with as kids. If you put two north poles together (or two south poles together) they repel each other, but if you reverse the orientation around, they then immediately attract each other and snap together. Well, this same behavior occurs at the the atomic level.
This is a water molecule and this behavior is why water dissolves things. It's called a dipole (two poles).





Here is a cool video describing this behavior of the electrons which makes this all possible. The pull of these poles is so strong that they can disassemble other molecules.


You can also see the potential of two water molecules being attracted to each other if the (+) green ears of one is located near the (-) purple belly of the second. This behavior on a very basic level kind of illustrates the Van der Waals force.
Here is an illustration of the process of adsorption where the target dipole molecules in a fluid are attracted to the dipole of a submerged surface molecule.



You can see the whole molecule on top does not have to be ionized. the distribution of negative and positive charges around the molecule means that some parts of the molecule will be attracted to some parts of the surface molecules. So it doesn't matter if the target molecule is broken up and ionized or not. This is an example of inter-molecular attraction and this is how activated carbon or resins such as Purigen work. They have different target molecules because the shape and charge distributions of each type of molecule is different and the substrate material itself has a specific shape and character of charge distribution. The attraction that the resin exerts must compete with the attractive forces of other charged particles in the water (such as the water molecules themselves for example), so it's not automatic that just because a particle has a charge or is ionic that it will adsorb to the surface of the resin.

Here is another schematic of activated carbon adsorption of organic molecules and it shows the pore structure (activation) which gives it a greater capacity.





TDS only addresses the quantity of things that have been dissolved by the water, which includes solids and liquids such as acids. Dissolved substances can be polar, like acids or non polar, like oils and fats. The acid will have a greater effect on conductivity (movement of electricity)  than a less polar non polar materiall, but the effect on TDS will similar because it's still dissolved. So that's why there is a generic estimated conversion factor between the TDS reading and the conductivity reading, because it was determined by empirical means how much variance there is between the two measurements.

Hope this clarifies.

Cheers,


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## dw1305 (12 Sep 2013)

Hi all,
This is the post for "Purigen & Van de Waal's" forces - <Can Purigen Strip down useful nutritients? | UK Aquatic Plant Society>.

You could potentially have a high TDS (but low electrical conductivity) in water with lots of humic compounds, in something like Rio Negro "black water". TDS is properly measured by evaporating a known volume of "water" to dryness, and weighing the residue. This is the reason that you know that TDS meters aren't measuring TDS.

I like conductivity as a measurement because it is straight forward, repeatable and a linear scale. All the other parameters have some factor(s) that complicate measurement. 

cheers Darrel


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## Ady34 (12 Sep 2013)

ceg4048 said:


> Hmmm...I can see immediately that we need to delve into our remedial chemistry.
> 
> OK look, can you see the little bunny rabbit below?
> This is a schematic of a water molecule.
> ...




Have to disagree.....Clive that is clearly a mouse with green ears, not a bunny rabbit!



very informative thereafter.


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## BigTom (12 Sep 2013)

Ady34 said:


> Have to disagree.....Clive that is clearly a mouse with green ears, not a bunny rabbit!
> 
> 
> 
> very informative thereafter.


 

I've just finished a PhD studying mice, and can confirm this.


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## Tim Harrison (12 Sep 2013)

Guys...I hate to sound like Jeremy Paxman, but humour me and apply the 101 chemistry - give me your opinion just to round things off nicely...is it theoretically possible - yes or no...
Following a similar train of thought, could it be that it is entirely possible for EC to remain constant and for GH to increase without carbon or absorbent resins?
Could it be for instance, that processes like plant uptake, and denitrification taking place in our aquariums - vastly augmented by powerful filtration - are constantly removing other dissolved solids capable of affecting EC at a similar relative rate to that which others like magnesium and calcium are entering in to solution, from say dissolving rock?
Presumably, over time an equilibrium will result, and should it be disturbed by a water change, for example, a negative feedback loop will ensure a return to homoeostasis. Hence, rising GH with a constant EC, as in Lindy's tank. Or am I still missing something crucial?
By the way Lindy, the rock you're using looks like chert of some sort, so it is largely composed of inert silica. However, it looks like it also contains some limestone type material which could conceivably dissolve and contribute to a higher GH.


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## dw1305 (12 Sep 2013)

Hi all,


Troi said:


> is it theoretically possible - yes or no


No. if the dGH is higher you must have more divalent cations (Ca++, Mg++). Your TDS meter measures conductivity and there is a linear relationship between dissolved ions and conductivity. If you have a higher dGH, you must have a higher "TDS".

The only case where this wouldn't be true was if you had a substance with a high CEC, where it would exchange cations dependent upon their relative abundance and position on the lyotropic series. In this case divalent ions are more strongly bound than monovalent ones, so Ca++ would be more strongly bound than K+ etc, and the dGH would fall why the TDS remained largely the same.

cheers Darrel


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## Tim Harrison (12 Sep 2013)

Yep got that...I think we maybe at cross-purposes...I understand there is a linear relationship between dissolved ions and conductivity. I also understand that conductivity combines all ions in the measurement. So it is possible for two different solutions to have the same conductivity but different dGH.

What I'm stating is that given the number and frequency of inputs and outputs in our aquariums it is possible to have a turnover of different ions in the same tank over time, some of which affect hardness, without necessarily increasing conductivity, as in the two separate solutions above. 

I don't think it necessarily follows that conductivity will continue to rise in a healthy well balanced aquarium indefinitely, at some point it will reach equilibrium as it does in many other systems. For instance, waste water treatment wetlands can reduce conductivity through the process of denitrification; the conversion of NO3 into diatomic molecular nitrogen (N2). A process I believe that is also going on in the filters and substrates of our tanks. Therefore, it is possible, for instance, for N03 to be replaced by bivalent cations (from any given source) in a ratio that does not affect conductivity but nonetheless affects dGH.

And I'm proposing that this could have happened in Lindy's tank through some mechanism or other. Hence the resultant and tortuous discussion on van der valk forces, resin, and carbon.


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## dw1305 (12 Sep 2013)

Hi all,


Troi said:


> I don't think it necessarily follows that conductivity will continue to rise in a healthy well balanced aquarium indefinitely, at some point it will reach equilibrium as it does in many other systems.


 Conductivity will carry on rising until ions begin to precipitate out of solution as salts. It is true that N2 could be out-gassed, but that is a special case. The only way that you could lose (and gain) Ca++ or Mg++ ions is as compounds precipitate out of/go into solution. This may be a pH mediated effect (with carbonates for example). You see this effect every day if you add CO2, as the added CO2 changes the CO2 ~ HCO3 equilibrium. You can also see this if you add calcium hydroxide, sodium carbonate or sodium hydroxide to carbonate rich water as calcium carbonate is precipitated, there is a more complete explanation here:<British Cichlid Association • The place to talk about the Cichlids in our Aquaria>.

cheers Darrel


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## Lindy (12 Sep 2013)

I'm still not entirely clear as to what is going on in the tank but thank you for the chemistry lecture, reminds me of college. Didn't know you could get a PhD for studying mice, I kept them as pets for a number of years and now feel a bit short-changed.


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## BigTom (12 Sep 2013)

ldcgroomer said:


> I'm still not entirely clear as to what is going on in the tank but thank you for the chemistry lecture, reminds me of college. Didn't know you could get a PhD for studying mice, I kept them as pets for a number of years and now feel a bit short-changed.


 

You have to measure them a lot, or it doesn't count.


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## Lindy (12 Sep 2013)

Ahh, damn, lol...
The last ones all grew massive tumours which were removed and they looked like little Frankenstein mice with all their stitches.


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## Tim Harrison (12 Sep 2013)

dw1305 said:


> Hi all,
> Conductivity will carry on rising until ions begin to precipitate out of solution as salts. It is true that N2 could be out-gassed, but that is a special case. The only way that you could lose (and gain) Ca++ or Mg++ ions is as compounds precipitate out of/go into solution. This may be a pH mediated effect (with carbonates for example). You see this effect every day if you add CO2, as the added CO2 changes the CO2 ~ HCO3 equilibrium. You can also see this if you add calcium hydroxide, sodium carbonate or sodium hydroxide to carbonate rich water as calcium carbonate is precipitated, there is a more complete explanation here:<British Cichlid Association • The place to talk about the Cichlids in our Aquaria>.
> 
> cheers Darrel


 
Agreed, but doesn't that assume the input of those particular bivalent cations is consistently greater than their output? Surely that's not always the case? Nevertheless, labouring my assertion is starting to feel like I'm pursuing the supreme quest of alchemy - transmuting lead to gold...It may be a watered down version of my original hypothesis (no pun intended), but I still reckon it's possible for conductivity to remain constant over time whilst dGH fluctuates due to changes in ionic composition through natural or artificial processes.


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## Tim Harrison (12 Sep 2013)

ldcgroomer said:


> I'm still not entirely clear as to what is going on in the tank.


Me neither - you're obviously unique...


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## dw1305 (13 Sep 2013)

Hi all, 





Troi said:


> Agreed, but doesn't that assume the input of those particular bivalent cations is consistently greater than their output? Surely that's not always the case?


Yes, you can deplete the calcium and magnesium in a number of ways, there are biotic processes, they could be incorporated into growing plants and the shells of molluscs, and there are biotic/abiotic chemical processes. Any ion can potentially form new compounds, the likelihood is dependent upon how reactive they are. 

If you just topped up the evaporation from a tank of hard tap water with further tap water, eventually you would reach equilibrium, where any further ions couldn't go into solution, conductivity remained constant and precipitation occurred. You can see this in the lime scale left as hard water droplets evaporate. The water volume falls and salts are deposited, in this case calcium carbonate first because it has low solubility.


Troi said:


> but I still reckon it's possible for conductivity to remain constant over time whilst dGH fluctuates due to changes in ionic composition through natural or artificial processes.


Theoretically it certainly could. In the lyotropic series you get the sequence NH4+ Na+ > K+ > Li+ > Mg++ >Ca++ <Hofmeister series - Wikipedia, the free encyclopedia>.  This means that we can precipitate insoluble calcium and magnesium compounds by adding more reactive monovalent alkaline metals <Common-ion effect - Wikipedia, the free encyclopedia>. This is how salt (NaCl) based ion exchange water softeners work. In this case dGH would fall, while conductivity remained much the same.

cheers Darrel


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## Lindy (13 Sep 2013)

Maybe I should clarify- My tap water has a gh of 3 and tds 45ish. I add mosura mineral plus to bring gh up to 5 (tds 117ish). Then i use mosura tds up, to get tds 150, which is supposed to raise tds without raising gh. So far this system has been working really well in the 54l. I do exactly the same for the cube but the gh keeps going up to 8. Some of the rock appears to have a whitish vein running through.


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## dw1305 (13 Sep 2013)

Hi all, 





ldcgroomer said:


> Some of the rock appears to have a whitish vein running through.


 Could be calcite, the "Mosura TDS up" is probably sodium based, so it would be very soluble and add TDS but not dGH.

I'd be very interested in the chemical breakdown of "Mosura TDS up", as my suspicion would be that it is a very expensive way of mainly buying sodium chloride (NaCl).

cheers Darrel


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## Lindy (13 Sep 2013)

I could send you some if you like, how much would you need to test it?


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## Lindy (19 Sep 2013)

After all of the interesting banter I decided to put a lump of the rock in a pint glass(classy) and test the gh every couple of days.  The result? the rock has not raised the gh.
Go figure..


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## sparkyweasel (19 Sep 2013)

Did you fill the pint glass with tank water or tap water?


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## Lindy (20 Sep 2013)

Tap water, the same water I put in the tank but without the shrimp additives


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## sparkyweasel (21 Sep 2013)

You could try it again using water with additives, in case the additives are reacting with the rock in some way.


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