Aquaponic Gardening

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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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Before the advent of synthetic chelates, hydroponicists used to utilize ferrous sulfate as a source of iron in their nutrient solutions. It is non-synthetic and allowed by OMRI when used as a "Crop Fertilizer or Soil Amendment".

It is also not chelated, so using it in high pH systems may not be a 'winning strategy'...but it is an OMRI approved source of iron. 

Vlad - minor correction.  Under the National Organic Program, ferric oxide, ferric sulfate, ferrous sulfate, iron citrate, iron sulfate, or iron tartrate may be used to correct documented deficiencies of iron. 

I.E. Must test and document deficiency before use. If you're following the letter of the law.

Right. As with many items, there are specific protocols to follow under NOP rules.

I was just trying to address question of 'are there other OMRI approved sources of iron'...I run across many gardeners who aren't in the NOP in terms of obtaining Organic certification...but do look for the OMRI label when purchasing inputs 

Thanks. I'm trying to go commercial and thinking I really need the organic certification if I am to make money, at least for selling to whole foods and such. Selling locally I'm pretty sure the people around here don't care, but 60 miles away in Austin Organic is the big thing.

Leads me to a second question, how do you test for iron and what should the levels be?


If you check out my blog - - I have a roundup of aquaponic-appropriate water test kits.  

A good level for iron is 2.5ppm

Thanks. I'll bookmark it for reference and take a look

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