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Can rock raise GH without raising TDS?

Lindy

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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.
 

Lindy

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

Tim Harrison

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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.
 

dw1305

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Hi all,
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.
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
 

Lindy

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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.
 

dw1305

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Hi all,
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
 

Lindy

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

Lindy

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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..
 

Lindy

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

sparkyweasel

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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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