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Evaporation and the pH profile (ie. CO2 levels)

Hi all,
jaypeecee said:
Perhaps one of the difficulties in keeping healthy plants arises because we try to use water that is low in bicarbonates ('low' KH). As Diana Walstad* points out: "...plants that can use bicarbonates (in addition to CO2) have an enormous advantage in alkaline water"............
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I think part of the reasons why Diana Walstad was keen on having water with a lot of carbonate hardness was that, when she wrote <"Ecology of the Planted Aquarium">, she wasn't advocating a filter, or water changes, so she needed a <"reservoir of hardness to counter "old tank syndrome".>

I think subsequently she revised her initial suggestion to include both <"water movement and water changes">.
jaypeecee said:
......Apparently, half of the aquatic plants tested** (almost thirty years ago) can use bicarbonates. I translate that to mean I may be better off using plants whose natural habitat is hard water.
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This is back to our old friend the <"CO2 ~ pH ~CO2 equilibrium and Total Inorganic Carbon (TIC)">, but whatever form that TIC takes the plants <"will always use it as CO2">.

I've always used <"relatively soft rain water"> and I think the consensus of opinion would be that <"low dKH allows you to grow a wider range of plants">.

cheers Darrel
 
Hi @dw1305
dw1305 said:
I think part of the reasons why Diana Walstad was keen on having water with a lot of carbonate hardness was that, when she wrote <"Ecology of the Planted Aquarium">, she wasn't advocating a filter, or water changes, so she needed a <"reservoir of hardness to counter "old tank syndrome".>
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I have the third edition (2012) of Diana Walstad's book, this being the latest edition. But, I'm not clear why the quote I gave from her book is now invalid. And I don't see the relevant connection with the need for a 'reservoir of hardness'. I bought Diana Walstad's book on your recommendation. I'm obviously missing something here. Would you mind explaining this for me, please, Darrel? I really want to understand this.

JPC
 
jaypeecee said:
Sorry.....and perhaps CO2 injection isn't necessary with hard water?
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It's not necessary at all 🙂
It can give faster growth. And more pruning and maintenance. 🙂
And it can help to grow plants fully submerged when the species would naturally grow emergent, or periodically alternating between submerged and emersed.
It's easy enough to let your plants grow naturally, you just have to accept the limitations.
 
Hi @dw1305

I can just about follow Clive's post to which you referred. But, the results from one of Diana Walstad's own experiments clearly demonstrate that some plants do grow much better in alkaline hardwater. She shows a photo in her book where she had Vallisneria spiralis grown under two different conditions. One was hardwater with alkaline desert soil, the other was in softwater with acidic peat substrate. The first of these plants grew very well whilst the second plant disintegrated. Figure VII-3 in her book refers. Is there, perhaps, some other explanation for her observations other than water hardness? Is the difference in pH the more likely explanation? I don't know but I would welcome any comments from anyone on this.

And, if people reading this are thinking that it is just science for science's sake, no, it isn't. If there's a better way of delivering carbon to our plants than using CO2, just think of all the advantages that could potentially bring.

JPC
 
Hi @sparkyweasel
sparkyweasel said:
It's not necessary at all 🙂 It can give faster growth. And more pruning and maintenance. 🙂 And it can help to grow plants fully submerged when the species would naturally grow emergent, or periodically alternating between submerged and emersed. It's easy enough to let your plants grow naturally, you just have to accept the limitations.
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Thanks ever so much for the feedback. May I ask what the limitations are? Do I need to ensure that the plants I choose are suitable for hard or soft water?

TIA.

JPC
 
Hi all,
jaypeecee said:
And I don't see the relevant connection with the need for a 'reservoir of hardness'.
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Diana Walstad had to use calcareous soil and hard water in her tanks to provide the carbonate hardness needed for nitrification. Because you didn't change any water that hardness wasn't replenished by water changes. Because she had hard water the pH would always be above pH7, and the TIC would always be in the form of HCO3-,.

She had to use plants that could use HCO3- as their carbon source, because there wasn't ever any free CO2 available.
jaypeecee said:
I bought Diana Walstad's book on your recommendation.
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I recommend every-one buys a copy, there still hasn't been anything written of similar scope.
jaypeecee said:
one of Diana Walstad's own experiments clearly demonstrate that some plants do grow much better in alkaline hardwater
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They do, <"Vallisneria doesn't like life in the tanks">, but grows well in our tap water (about 17dKH & 17 dGH). It maybe an <"iron toxicity effect etc.">, rather than directly related to pH/dKH.
jaypeecee said:
Do I need to ensure that the plants I choose are suitable for hard or soft water?
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Most "easy" plants won't care either way.

cheers Darrel
 
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Yes, or those that are not fussy about hardness.
Any that are classed by suppliers as needing high CO2 will probably struggle without injection, unless they have access to the air.
For example, I like Japanese Rush, but it does not do well completely submerged, some say you can't grow it in a tank. But if you let the tops of the leaves stick up above the surface they are fine.
 
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