hoppycalif

Very good idea! I'm not sure why it was considered important to add clay to mineralized soil, so I'm not sure if STS meets the need. As I recall, it was iron-rich clay that was recommended, but Diana Walstad has pointed out that ordinary dirt contains a significant amount of iron anyway. (I'm too lazy to read 58 pages here to find out why the clay.)

GadgetGirl

I don't remember Diana ever mentioning adding clay. At least I can't find it. But she does discuss problems with iron toxicity. Seems like that kinda just popped up somewhere about adding red clay as an iron source.
Also, I'm pretty certain montmorillonite clay (STS/OilDri) is not a source of iron. STS is used in the substrate to bind nutrients because of its high CEC. Pottery clay and montmorillonite clay are two different materials to the best of my knowledge.

mistergreen

Plants can't use the iron clay anyway. It's bonded with the silica. Plant roots can get iron ions attracted to clay & soil, CEC.

Montmorillonite clay is like 3x higher in CEC than pottery clay.

Latka

I found bentonite clay powder in the department store facial care section. Does bentonite clay have a high CEC level?

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GadgetGirl

I use VERY small amounts of powdered calcium bentonite every few days. Like barely a pinch in a 10 gallon tank just added to water. Supposedly it absorbs toxins and provides a few minerals among other things. Koi breeders have been using it for years. (https://allnaturalpetcare.com/blog/2...aquarium-fish/). I don't think it has any CEC value. It has a totally different purpose and form than STS or OilDri and you would never use it in the volume that we do STS! STS or OilDri are very large particles that take a very, very long time to dissolve, if ever. The product you are referring to is a very finely ground powder as people consume the food grade type (which is what I have). You really can't compare the 2 products.

mistergreen

yes, betonite is a type of montmorillonite clay. They're all the same really in structure.
Make sure it's 100% clay without added cosmetic stuff.

mistergreen

STS & Oildri goes through a process of drying, shaped, sized, and firing (like pottery but not exactly) so they don't dissolve in water. Bentonite & montmorillonite clay are the same stuff.
The powdered form has more surface area than the baked form.

Latka

According to Walmart website, this is sodium bentonite, not calcium, but otherwise pure.

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Latka

Thanks for the input, GadgetGirl. That web page is very informative. I can see where calcium montmorillonite may be better than the sodium type as an aquarium supplement.

MisterGreen, I think the fine grained nature of this facial cosmetics clay may make it a good choice for blending into the soil substrate for CEC value. It seems a little will go a long way. I wonder if sodium bentonite in the substrate will increase the sodium content of the water.

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mistergreen

It doesn't look like it's water soluble so you should be fine. You can buy a big bag of Safe-t-sorb or Oildri for $9. Bang for your bucks.