Richard bray

Clay Pebbles
These pebbles are the easiest media to work with because they are light and smooth.
Clay pebbles are also referred to as LECA (lightweight expanded clay aggregate), and they are basically popped clay. Clay is mined and farmed into balls, which are then superheated in a kiln to over 2000° untill the clay pops, giving it a light, porous structure.
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The most common LECA used for aquaponics is Hydroton. These pebbles come in 50 lb bags, which will fill roughly 2 cubic feet. They are lightweight, so shipping them is much easier than transporting river rock or lava rock.
Clay pebbles are reusable, and provide a smooth surface that does not damage roots. However, they do float for the first few months, and this can cause clogs. You can help prevent this by soaking your pebbles is water for 24 hours before putting them into the grow beds. Make sure the water you use is close to pH neutral and does not contain any harmful chemicals.
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River Rock
Although this is the most expensive option, it is also one of the most popular for grow beds. Costs will vary depending on the supplier, but river rock is generally available at hardware stores and landscape supply companies.
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itver rock is not porous, but it still has enough surface area for beneficial bacteria to colonize and thrive. It's smooth, which makes slanting and harvesting much easier than lava rock, and it doesn’t float like Hydroton.
The biggest drawback to river rock is the weight. Systems that use river rock as a substrate will be permanent. One cubic yard of river rock (27 cubic feet) weighs 2,600 lbs. The average 4’ x 8’ x 14" grow bed will need about 37 cubic feet of media, meaning a bed full of river rock will weigh almost 3,600 lbs.
If you choose to use river rock as a media, rinse it before adding it into your system. River rock is usually coated in a limestone dust, which can raise the pH of the water and harm your plants. Also, the bust and debris that accumulates in piles of river rock at supply companies may cause problems in your system.
Test river rock before you purchase it to see if it will affect the pH of your system. Take a bottle of vinegar and a cup, and fill the cup halfway with rock. Fill the cup with vinegar, and look for fizzing. If it fizzes, the rock has a high pH, and you will want to find another supplier. If the vinegar does not fizz, the rock is pH neutral, and it should be suitable for your system.
The best size for river rock is a 1” median diameter. Too large, and there won't be enough surface area for bacteria to colonize, and the water won’t be aerated properly. Too small, and roots may have difficulty finding space to grow.
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