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Hardscape stone and hard water

Glenda Steel

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I am hoping to use rock for the first time in an aquascape and wanted some advise please. We are in an area of the UK which has exceptionally hard water (according to the local waterboard my postcode has a reading of 324ppm, a GH of 18.4 and a high ph of 7.35) is there a stone that won't raise the hardness any further?
 

dw1305

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Hi all,
is there a stone that won't raise the hardness any further?
Yes, basically it is all of them.

The exception is when you add CO2.

If you add CO2 the pH will fall, if you add enough CO2 to get below pH7, softer limestone will start to dissolve. Have a look at <"this thread"> for a more complete explanation.

If you are worried, <"rounded cobbles"> are always pretty safe, because only hard rocks form rounded cobbles.

You can tell that hard water doesn't dissolve limestone by the huge shell beds (below) that have built up over millennia in Lake Tanganyika.

shell-dweller-3.jpg


Technical bit
Limestone (calcium carbonate - CaCO3) is only soluble in weak acids, it isn't soluble in pure water. Rain-water (pure H2O) is a weak acid, because as it falls a very small proportion of the dissolved CO2 becomes carbonic acid (H2CO3), and that then disassociates into H+ (proton) and HCO3- (bi-carbonate) ions. Acids are defined as "proton donors", and we've gained a proton.

When the rain falls in an area with limestone geology, the rain-water rapidly dissolves away a fragment of the rock and the carbonate ion (CO3--) neutralises two H+ ions to give two HCO3- ions. This process usually continues until the ground water is fully saturated with HCO3- ions and the water is "very hard" with a dKH of ~18. This is the situation for most the Southern and Eastern UK.

Because most of our limestones are fairly pure CaCO3, dKH and dGH will be the same (they are <"both defined in terms of CaO">).

cheers Darrel
 

Glenda Steel

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Darrel thank you for taking the time for such a detailed response! So basically this will only apply if I add higher levels of co2 but does it make a difference if I intend to keep the rocks clean of algae by using a wire brush during maintenance? I will keep the filter running and I now do a routine 50% water change weekly. With regards to the type of rock, I was hoping to aquascape an Iwagumi (my first!) and although I have seen some using smooth pebbles I was really hoping for a more traditional approach perhaps using Dragon stone. Yes I do intend to use co2 (again for the first time) but only minimal amounts (I think - advice needed on that too!) as I'm hoping to use a carpet plant such as Micranthemum sp. "Monte Carlo" and Echinodorus tenellus. I have also read that certain aqua soils buffer the water hardness and ph, do you think this would be enough to avoid creating unbelievably hard and uninhabitable water?
 
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dw1305

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Hi all,
but does it make a difference if I intend to keep the rocks clean of algae by using a wire brush during maintenance?
No, even if you are exposing new surfaces all the time the rock won't dissolve, because the water is already saturated with HCO3- ions.

If you add enough CO2 to lower the pH below pH7, the exposed rock will start to dissolve. Once you stop adding CO2 the pH will rise again and the 2HCO3- and Ca++ ions will precipitate back out of solution as CaCO3, but as a fine powder.

If you have snails their shells will begin to dissolve first, because <"biogenic calcium carbonate"> (aragonite) is slightly more soluble than calcite. There is a more complete explanation in <"Nerite Snails in high tech."> (from the bottom of page 2. onwards).

cheers Darrel
 

Glenda Steel

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Thank you so much Darrel, I do have Nerite snails and was planning this co2 injected tank as being a shrimp tank. I have now read the suggested posting and wonder whether I actually need co2 at all, particularly as you say you don't use it! Do you (or other members) know whether the Micranthemum sp. Monte Carlo and Echinodorus tenellus work grow well without co2 injection? I presume liquid carbon has the same effect or perhaps more concentrated effect? It would account for the loss of one of our Nerites shortly after I started using it. I no longer use it as I am not comfortable with the effect it was having on the rogue snails. Last question: what do you do for a living Darrel, I hope you don't mind me asking?
 
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sparkyweasel

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Hi Glenda, before a house move I had Echinodorus tenellus growing very well without CO2 injection or liquid carbon, and my tap water was 17DH, not much different to yours. I used to take a handful out once a week. Sadly I don't have it now, or I could have sent you some. :)
That was a cherry shimp tank and they did well too, and seemed to like the E. tenellus.
I never tried Monte Carlo though.
 

Glenda Steel

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Hi Sparkyweasel (love that one!) that's brilliant news re the Echinodorus and such a kind thought!!! Good to know the shrimp liked it too. I really do think I may stay low tech (we have one tank already low tech) as the thought of pressurised co2 is a little daunting. Many thanks for the reply!
 

Jayefc1

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Hi just a quickie for the first time about a month ago I cleaned my glimmer wood rock (i delive this is a soft lime stone after research)with a wire brush did a 50% water change went out for dinner come home to find all my cherry shrimp at the top of my wood in huge distress so have never cleaned with a wire brush again just a soft rub with a tooth brush I have co2 and my ph does drop from 7.4 to 6.4 during injection but apart from that one time never had a issue
 

Glenda Steel

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Thank you for letting me know Jayefc1, I will take note and am happy to give the rocks a clean (with a toothbrush) more than once a week if required rather than be more aggressive with a wire brush.
 

Jayefc1

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Im sure it depends on the rocks as I've seen George farmer use a wire brush his vid gave me the idea but won't be doing it again lol
 

Glenda Steel

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Perhaps it also depends on the size of the tank and amount of water to dilute the residual amount of debris after the water change?
 

dw1305

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Hi all,
particularly as you say you don't use it!
I'm not a CO2 user, I was primarily interested in plant (really plants/microbe) biofiltration as a technique for improving the <"quality of waste water">. If you can avoid oxygen limitation you can use plant/microbe filtration to radically improve the quality of polluted water. From there it was a small conceptual leap that you can use the same techniques to "polish" the quality of relatively clean water.

I'm still not interested in optimal growth, ideally I want <"slow, but active, growth">. The <"Duckweed Index"> is a way of using the growth of a floating plant to estimate nutrient status, and because it is a floating plant this takes CO2 limitation out of the equation.
Echinodorus tenellus work grow well without co2 injection?
<"Helanthium (Echinodorus) tenellum"> is fine without CO2.
Last question: what do you do for a living Darrel, I hope you don't mind me asking?
I look after a teaching lab. at one of Britain's smaller Universities.

cheers Darrel
 

Glenda Steel

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Firstly the students you teach are very lucky to have such a knowledgeable and helpful lecturer Darrel! The Duckweed index is fascinating and I love the idea of "constructed wetlands" to treat landfill waste water, the positive impact it must have on the surrounding nature is invaluable. I agree re the plant growth and will settle for healthy over fast/out of control any day! I ran into so many problems with my very first aquascape (shown on my profile pic left) as the Vallis' took over and as a beginner I didn't know how to handle it, the result has been a 3 year battle with every algae under the sun! Around a month ago I stopped using chemical "polishers" and liquid carbon in favour of a complete liquid plant food (up until then I had shied away from ones using nitrates and phosphates for fear of algae) the health of plants and the clarity of the water improved immeasurably. I am now trying to make sure I create a far more balanced aquascpe for both my first and now second tank. I really can't thank you enough for your advice and I am now convinced and confident to go low tech with our 2nd tank too.
 

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