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Frustrating GH rise

Aktasak

Aktasak

Member
Joined
5 Dec 2024
Messages
41
Location
UK
I’m going to start with saying that I have absolutely nothing in the tank that could contribute to a GH rise, the only rocks I have are lava rock and I’m using this soil: Flora First Aquatic Planting Substrate Brown plus a small section of sand which was recently changed to a soft sand after discovering that WIO Cimarron sand was messing with Kh a bit.
I use RO water and had recently gotten my hardness levels down to where I wanted them and was going to begin doing water changes with remineralised RO but these have now come to a halt. 🙄

Last time I tested the gh and kh they were at 6(gh) and 5(kh), then I fiddled with some plants, moved them around etc. Can the disruption of soil cause the GH to rise? According to the API hardness kit, my GH is now at 10 but NTlabs says it’s at 8 and my KH is 6 on both, so I’m a bit confused on which one to believe 🫣.

Any advice is welcome!
 
Aktasak said:
I have absolutely nothing in the tank that could contribute to a GH rise
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But if you are measuring a GH rise, then there 'has' to be something in your tank that contains calcium or magnesium that is dissolving and adding to the GH levels.

You say you are remineralising your RO - what is your remin addition? have you double checked your calcs to make sure you're not adding too much to the water change water? Have you tested the GH/KH of the remin'd water? It's easy to make a mistake (I've done it many times myself), especially with the tiny quantities of salts involved that make large changes.

What ferts are you adding? Do they contain magnesium?

Finally it could be the cation exchange happening in your soil. If it started off with hard water the soil could have absorbed calcium and carbonates, and now the water is softer the cation exchange is working in reverse (though its not that soft at 6GH/5KH) - @dw1305 will be able to explain this process far better than I.
 
Hi all,
Wookii said:
Finally it could be the cation exchange happening in your soil. If it started off with hard water the soil could have absorbed calcium and carbonates, and now the water is softer the cation exchange is working in reverse (though its not that soft at 6GH/5KH) - @dw1305 will be able to explain this process far better than I.
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That was going to be my suggestion as well.

cheers Darrel
 
Wookii said:
But if you are measuring a GH rise, then there 'has' to be something in your tank that contains calcium or magnesium that is dissolving and adding to the GH levels.

You say you are remineralising your RO - what is your remin addition? have you double checked your calcs to make sure you're not adding too much to the water change water? Have you tested the GH/KH of the remin'd water? It's easy to make a mistake (I've done it many times myself), especially with the tiny quantities of salts involved that make large changes.

What ferts are you adding? Do they contain magnesium?

Finally it could be the cation exchange happening in your soil. If it started off with hard water the soil could have absorbed calcium and carbonates, and now the water is softer the cation exchange is working in reverse (though its not that soft at 6GH/5KH) - @dw1305 will be able to explain this process far better than I.
Click to expand...
So I haven’t used any minerals yet as I’ve been softening the water with water changes by adding pure RO.
For fertilisers I’m currently using TNC complete, I believe it does indeed contain magnesium.
 
Andy Pierce said:
"Leftover" ions in soil can last a very long time - months or more. I eventually lost patience with it and rescaped with sand. Problem solved.
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I would but this is the second rescape as I was using JBL aquabasis under the sand and it was raising my KH. 😆
 
Hi all,
Aktasak said:
Last time I tested the gh and kh they were at 6(gh) and 5(kh), then I fiddled with some plants, moved them around etc. Can the disruption of soil cause the GH to rise? According to the API hardness kit, my GH is now at 10 but NTlabs says it’s at 8 and my KH is 6 on both, so I’m a bit confused on which one to believe
Click to expand...
Do you have a conductivity (TDS) meter? It will <"cut straight to the chase">. If the conductivity is rising? You have ions going into solution.
Andy Pierce said:
"Leftover" ions in soil can last a very long time - months or more. I eventually lost patience with it
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I've been there as well, in my case <"with Tesco Moler Cat litter">.
Andy Pierce said:
I eventually lost patience with it and rescaped with sand. Problem solved.
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That is one reason <"I like silica sand">, it takes an <"unknown unknown"> out of the equation.

cheers Darrel
 
A TDS pen (£10) might alleviate some of the frustration with the tests. It tells you 'stuff' (total solids) in your water, so not specific to GH but gives you an instant electronic reading so you can see values changing more easily - it's also handy if you are remineralising as you can do one batch carefully measured/checked GH and then just remineralise to the same TDS.
 
Still battling it, it’s very frustrating.
The Kh and gh were at 5 but now both have risen to 7. Could it be the sand? Could the soil be leeching nutrients in the water column?
I’m so ready to throw in the towel. 😩
 
dw1305 said:
Hi all,

What does the TDS meter say?

It won't be the sand, unless it has shell fragments in it.

They could, but it would be via ion exchange.

Honestly it isn't worth worrying about.

cheers Darrel
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TDS is 130 at the moments, I think it was much lower.
The sand I believe is simply just plain old silica sand.
Will the ion exchange eventually settle after a while?
Thanks!
 
Hi all,
Aktasak said:
TDS is 130 at the moments, I think it was much lower.
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Just record the values over a couple of weeks, that will show if you <"have a consistent rise">.
Aktasak said:
The sand I believe is simply just plain old silica sand.
Click to expand...
Perfect, you can discount that as a source of ions.
Aktasak said:
Will the ion exchange eventually settle after a while?
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Yes and no. "Yes" the substrate and water will eventually reach equilibrium, and "no", because if the water parameters change noticeably the substrate will exchange ions with the water until a <"new equilibrium is reached">.

cheers Darrel
 
dw1305 said:
Hi all,

Just record the values over a couple of weeks, that will show if you <"have a consistent rise">.

Perfect, you can discount that as a source of ions.

Yes and no. "Yes" the substrate and water will eventually reach equilibrium, and "no", because if the water parameters change noticeably the substrate will exchange ions with the water until a <"new equilibrium is reached">.

cheers Darrel
Click to expand...
So, what can I do in the meantime? I’d rather they did not fluctuate but remain stable.
 
Hi all,
Aktasak said:
I’d rather they did not fluctuate but remain stable.
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They are always going to fluctuate, honestly it isn't the problem that the sellers of buffer etc will tell you that it is. That is why I always suggest a <"datum range of values">.

The only fresh water body that doesn't show much variation is <"Lake Tanganyika">, mainly because it holds a huge volume of very salts rich, almost infinitely buffered, water. Even the water chemistry of the Amazon river will vary dependent on what tributaries have merged, whether it is the wet or dry season, how much it has rained locally etc.

I wrote this ten years ago, but I haven't found any reason to revise it <"Setting up empty tank new project advice please">

In my opinion stability isn't really as important <"as resilience">.

cheers Darrel
 
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If the leeched hardness comes from the soil and you decide that you do want to stop it, you could raise the hardness of the water to the level that puts it at equilibrium with the soil, whatever that level is. Although if your soil is not leeching, yo will never get it to move towards a lower hardness equilibrium.

That being said, I'm with Darrel in thinking that you may not need to worry about it. Just let it do its thing. If you do constant and significant water changes, you will keep the hardness fluctuation at a narrow range, which should be good enough for most purposes.
 
I’ve been in the situation where I had fresh lava rock. For the fun of it I poured some HCl over some discolored bit, and it started reacting straight away. So carbonates were in the lava rock, so there might be calcium and magnesium in there as well.

I’m running my tank at KH 1.5 and GH 3, but despite the carbonates in the lava rocks, I still added them.

I’m with Darrel and LMuhles as well, for the reasons they mention.
 
PeerUnk said:
I’ve been in the situation where I had fresh lava rock. For the fun of it I poured some HCl over some discolored bit, and it started reacting straight away. So carbonates were in the lava rock, so there might be calcium and magnesium in there as well.
Click to expand...
Would it be worth testing some of my lava rock? I did test it before putting it in the tank using the nitrate #1 bottle from the api test kit and it did not react.
 
My Gh10 out the tap but after 3/4 days in the aquarium it raises to 13. I find dosing tnc complete does this aswell as my substrate
 
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