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does anyone have a Canadian source for calcium bentonite? I checked a local clay supplier, but they do not. The only thing I've found is Koi clay, but all the online suppliers are out.
 

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Personally, I'm not sure what the purpose of the bentonite is and am hoping Doug could jump on to explain. Obviously, calcium bentonite adds calcium, but as he explains way back on page 1 or 2, calcium carbonate is being added anyway. One of the main commercial uses of bentonite is for pond linings because the stuff is almost as impermeable to water as a rubber liner. The texture is horrible for building a substrate with pore spaces. Bentonite would boost the cation exchange capacity because redart clay is kaolonite clay with iron oxide. Kaolinte has a low CEC compared to other clays but it is still pretty good.

All we are doing here is creating a chemical sponge by using clay, and then filling that sponge with calcium ions. A redart clay and calcium carbonate blend should fit that bill nicely. Everything else should be toward creating the desired testure IMO. BTW, the reason I started with redart clay all those years ago was almost entirely for the look! Tropical rain forest soils tend to be well weathered kaolonite clays with high iron oxide content - which is what redart clay is. It seemed like a good place to start with replicating the substrates many dart frogs are in contact with in the wild. In truth, you could dose any high clay content substrate with calcium and get the mineral benefits. Many high clay soils will provide the benefit without calcium dosing. Any high clay soil from an area with hard water or limestone bedrock is likely already saturated with CaCO3 Matt Mirabelo took it a step further and just dosed a clay loam (I think) soil with iron oxide to turn it red. IMO, it looks even more like tropical soils because it has aggregates forming the 'crumb' texture that has so far eluded me.

I want to start experimenting with some new recipes to improve soil texture and possibly even eliminate the need to run the stuff through a mesh, but I'd really like to see and hear how aggregates have held up with Doug-based mixes over time first.
 

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Thanks for the detailed response Brent. I think the bentonite is used to give the clay more plasticity. To hold it together better.

What would happen if you were to fill the space between the dried clay cubes with a coarse beach sand (or well washed construction sand)? Would the clay and sand blend long term, or would the sand maintain the drainage channels between the clay?

If it blends over time, would that give you the soil texture you are looking for?

In the tropics, does water drain through the laterite soil or does it run along the surface? I always wondered about this last one.
 

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Thanks for the detailed response Brent. I think the bentonite is used to give the clay more plasticity. To hold it together better.
Hmm. Redart is very plastic by itself which is why it makes a good pottery clay. Bentonite is a lot more slippery though so I could see it making it easier to push the mix through a mesh which I've never tried to do. The stuff is like axle grease when it is wet so one of the least pleasant substances I've worked with. In fact, one of its many uses is as a lubricant.

Bentonite does have about 5-10X higher CEC than kaolinite through so it makes a much more efficient calcium sponge than redart alone. However, we are all just guessing about the nutritional benefits of clay soils and even and what levels of calcium adsorption are needed for any therapeutic benefit it provides. I think anecdotal evidence suggests there is something positive going on here, but we don't know if really supercharging the CEC is necessary to get the benefit. Or conversely, if it is possible to overdo it. I'm not saying bentonite is bad, it may have an important benefit, but it is a royal PITA to work with and counterproductive to some of the other properties. It's although worth mentioning that is wasn't part of the mix in my viv, and I was the first to report no more problems rearing pumilio froglets to adulthood after adding UVB and clay soil. I still couldn't say which is more important.

What would happen if you were to fill the space between the dried clay cubes with a coarse beach sand (or well washed construction sand)? Would the clay and sand blend long term, or would the sand maintain the drainage channels between the clay?

If it blends over time, would that give you the soil texture you are looking for?
I've considered that, but I think over time the clay would just was into the sand and fill the cavities. Then you'd have something more like concrete. In nature, fungi and bacteria secrete "glues" that bind small soil particles together into larger aggregates that lets the soil maintain an open texture. When I say 'pseudo sand' I'm talking about clay particles that are glued together into larger sand size aggregates. The soil is still clay and chemically behaves like clay, but the physical structure allows air and water to flow through it more like sand. The theory behind adding sugar and starch and then clumping or the media to force (temporarily) an open physical structure. We hoped the sugar and starch would supercharge growth of bacteria and fungi so they would 'glue' that hard-won physical structure in place so they didn't just dissolve into the voids over time.

I think using charcoal instead of sand in the mix could provide some additional benefits, but wouldn't solve the texture puzzle. What I've been thinking about lately is mixing corn cob kitty litter into the dry ingrededients (maybe as much as 50%) and forget about wetting, meshing, and drying. Just place the dry ingredients in the viv and mist it until is wetted. The thinking here is that the corn cob would keep the clay from dissolving into the voids, but over time, bacteria and fungi would break down the organic cob to leave open pores. Adding that much carbon would create one helluva fungal growth and likely look like ass for awhile, but could also build a whopper of a springtail population. However, it might be a solution looking for a problem if the sugar and starch addition in Doug's recipe has been effective in stabilizing that open structure. It could also be a giant flop.

In the tropics, does water drain through the laterite soil or does it run along the surface? I always wondered about this last one.
Of course we should be careful about over generalizing what "tropical soil" does but it does both. Compared to the fluffy soils we typically find in temperate forests and grasslands, these tropical soils are compacted crap and infiltration rates are nothing compared to rich organic soils. But they are open enough that water does infiltrate the soil (and remember there is a LOT of water to go around in those forests (at least for now). Also, there is an abundance of ants, termites and other critters constantly tunneling through. With the help of those microbial glues, they stay open longer. That creates a LOT more volume for subterranean arthropods to occupy. That's where organic substrates like ABG have clay substrates beat hands down, but if we can solve the texture problem, we'll be adding a lot more function to our clay substrates.
 

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I found this method for improvement of tropical clay soil for growing plants. Not sure if this idea is to bake it into a LECA like structure or just a hard drying process with wood charcoal added but perhaps with some experimentation a similar method can be accomplished. I read somewhere else that the fine powder is discarded perhaps because it reverts to a sticky clay substance. I also know that gypsum can be used to improve drainage in some clay soils but I'm not sure which clay soils are improved with gypsum. Another solution might be to just mix in a few clay chunks or a small amount of powder into ABG just to improve the mineral and Fe content.

Perhaps this article will provide the reason for how it works. Heating clay may cause it to expand permanently changing its structure. So perhaps passing the clay through a fine screen and heating it in an oven while still full of pores will accomplish what bbroch is trying to achieve. As for temperature I remember from my toxicology days that pyrolysis of wood occurs at 440 degrees F. So this may be the minimum temperature. Perhaps for an hour or two. This might cause permanent chucks of permanently porous clay that will still absorb moisture but will still drain readily and never clump together.

 
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