Frustrating GH rise

[Aktasak]

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!

 

[Wookii]

I have absolutely nothing in the tank that could contribute to a GH rise

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.

 

[dw1305]

Hi all,

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.

That was going to be my suggestion as well.

cheers Darrel

 

[Andy Pierce]

"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.