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Hello everyone,

I haven't found information about clay balls influence on GH so I start a new topic.

The thing is I have a GH problem since I started my system (four months ago) and I finally realized that the clay balls increase a lot the GH of my water. I ran some tests with osmose water twice and the results are clear. Within three days, a few balls increase the GH from 0 to more than 21°d (for half a liter of water).

I never heard about that before and I'm looking for a solution to decrease my GH or at least damp the influence of clay balls.

Any thought?



I have a indoor 200 L fish tank with a loop siphon growbed filled with clay balls. I currently have only one big goldfish.

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There is no calcium or magnesium in the clay balls your gh must be coming from some where else. I just tested this last week for a customer that suspected teh same issue and we crushed then tested 2 bags and couldn't not get it to raise the gh or even register much of any calcium or magnesium which makes up most of what your gh reading is. Id be more than willing to bet its your tap water. Anything will raise teh gh of R/O water because its strips absolutely everything out so its going to bind with what it can in R/o. Your gh isnt from your clay balls.

Hello Steve R,

I'm sorry I took such a long time to answer but thanks for your response.

My problem is that I tried with R/O water and not tap water. If your are so sure it's not the clay balls that are responsible (and you are the second one to tell me it is not possible), could it be possible that calcium and/or magnesium adsorbe itself onto the clay balls surface? And then when I run my test, the Ca and Mg are simply released into my water?

One detail I forgot to mention is that the clay balls I used for my test come from my system who has been running for a few months now.

Thanks for your answer


What brand of clay balls? And who's the manufacturer?

I'm gonna check that and come back to you.

But now I'm quite sure that my problem doesn't comes from my clay balls. I checked the influence of clay balls on R/O water but the balls I used came from my running system. As the clay has a strong ion-exchange capacity, I think that Ca and Mg were simply adsorbed onto the balls in the system and when I put them into pure water, there were quickly released into the water. That could explain why the total hardness I measured in the R/O water with the clay balls was so high.

(I hope I'm clear enough).

Anyway I will try to find a drinking water filter to gradually decrease the hardness of the water. 


Remind me....why are high GH levels a problem in an aquaponics system? Does it affect plant nutrient uptake?

For what I understoot, high GH levels can impede the iron and potassium uptake. For instance I my case I can clearly observe an iron deficiency and I think this is due to the high GH level.

For the fish, it doesn't seems to be a problem (my goldfish seems happy with all the Calcium around him).

Ok so I checked a little bit the reason for this nutrients uptake limitations and the answer is quite simple actually.

Calcium and Magnesium reduces iron assimilation because they compete with each other. Calcium has 2 positives charges, such as magnesium and iron. The plant is not able to differenciate them so if the water is full of calcium and has a normal iron concentration, it will be easier for the plant to absorbe calcium than iron.

I recommend getting an iron test kit.. with out testing your levels, its impossible to know if you even have any iron in the system..

ive been trying to document my use of iron and have been amazed how much is needed and how often.. literally, the plants can use up 300 mil in a 250 gallon system over night!! ..that's a lot of iron!! same with Mag

you really need a Mag test to check the Mag levels too. ive found that Magnesium is often the problem, and it with look like an iron deficiency.

Biomin Powdered iron -

Hanna iron test -

Hanna Mag test -

Rob - are you using that Biomin powdered iron? I hate to break it to you, but that product is very very weakly chelated. It's chelated with citric acid, which is 7 times less stable than Fe-EDTA, and loses all stability over a pH of 6.3ish. So the plants aren't using it all up - it's just falling out of suspension.

Ha!! even worse!! im using the biomin liquid iron.. and your right, it doesn't hold up at all, the system with the higher ph is ugly as all get out... im going back to the sprint 330(works in high ph). the liquid biomin is great for foliar spraying.
I had been using biomin liquid iron and came across this researching their powder.

Is there an omri approved iron that works better? Thanks

synthetic chelators are expressly forbidden by the national organic program. 

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