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Finding gravel seemed like the easiest thing to do. Run down to the local gravel pit and pick up a cubic yard. But, gravel is heavy it runs 110 lbs per cubic foot, and can be sharp, cutting your hands when planting in it. So the search began for the better alternative. Expanded Clay (Hydroton or Leca) was the recommendation. I called all the local supply houses in Utah, nobody carries it or an equivalent expanded clay. I called several national suppliers, they carry it. So checking into having it shipped Utah, no problem just $1,000 dollars for a pallet!!! Well that wasnt going to work.
In searching around I discovered a company in Utah that manufactures Expanded Shale www.utelite.com Shale by nature is an Alkali not neutral like clay (Hmmm). It comes in various sizes, but the 3/8 medium 10mm looked the best. (I have since wished I used the 1/2-3/4" as 3/8" works but is to fine.) Shale is quarried from the local mountains and heated and in their words,
As the raw shale passes down the length of the kiln, the material is heated to a temperature of approximately 2000 degrees Fahrenheit.
At this temperature the shale is red hot and somewhat plastic. Internal gases trying to escape the shale expand or "bloat" the particles, creating a myriad of small non-interconnecting internal voids. These voids are retained after the material cools and solidifies.
Sounds like the perfect media. It weighs 55lbs per cubic foot (Hydroton ways 45-50lbs per cubic foot). Light weight, lots of voids for stuff to grow in, cleaned and washed.
In researching the product, it has been used in water filtration and water reclamation doing just what we do, growing bacteria. Water quality tests showed that water passed through the gravel came out meeting drinking water standards. No excessive levels of trace minerals or toxic chemicals.
A study conducted in Koi pond, showed that when unwashed expanded shale was put in the pond, the first week the PH spiked up to 8.0-8.5 then settled down to 7.5-8.0 within a few weeks. They also said that the shale has a tendency to bond with phosphorus, which is good for water cleaning, but may be an issue in aquaponics, we will see.
I made the 1-hour trip to the plant and hand shoveled a yard and half into my small-enclosed trailer. The material was clean, (no dust, no fines) and easy to shovel. It is angular as it has been crushed, but not sharp, as the heating process tends to blunt the sharp edges. Also very important, it only cost $26 a cubic yard (close to a cubic meter), which is all I needed for my system and A LOT nicer than $1,000.00.
This weekend I hope to give it a quick wash, and then soak it in a solution of phosphoric acid to try and do 2 things. 1) Allow it to take up phosphorus so that it leaches less out of the aquaponics system water and 2 to bring the PH down a little to begin with. Then Ill run the system for a few days, flush it and refill with fresh water to start the cycle process.
My hope is that over time the natural tendency of aquaponics PH to drop, will be buffered by the shale, and a PH of 7.0 or so can be maintained without added material. Im very curious to see how it goes.
After 4 hours of washing and bucketing, the gravel is in. The first problem was the large screw on cap from the IBC Totes has hidden vents - LEAKS. I had to dig out the gravel, unscrew the cap, dry the whole thing and reseal with aquarium silicon and wait 24 hours before getting it wet. The other challenge was the tank cage made of metal. The uneven pipe base caused me to have to move around the support beams (after the other tote was filled with gravel!). Always position everything before filling! Now after 6 hours of work, I had 2 grow beds (almost done), with installed bell siphons, almost ready to go.
The attached pictures show:
1) Drain and Siphon view
2) The problem cap, now sealed with silicone
3) Beds almost ready.
4) Expanded Shale.
Although the shale looks like common river gravel, it is not. It has been crushed, filtered, heated. Even after hand working, washing, dumping this shale, my hands are not chafed or cut. The sharp edges were melted by the heat and the shale is full of bubbles and voids. So far, I'm very impressed with the expanded shale, its light, cleaned easy - now if it will just grow crops and not kill fish...
Next time the search for heating, cooling and what pipes to use.
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