Growing Edge Part 4: Aquaponic Grow Media

This is a reprint from this month’s installment of the series on Aquaponics I’ve been writing for Growing Edge. Hope you find it useful!

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If you have been following this series on how to build a media based aquaponics system, you now have your fish tank and grow bed, and they are interconnected by flood and drain plumbing which is ready to be powered by a pump. Now let’s talk about the environment for your plants – the grow media . aquaponic grow media
Most people use either gravel or expanded clay for their aquaponic grow media and both are widely available. However, there may be other candidates, depending on what is available in your area.

Here are some ‘must haves’ and ‘nice to haves’ for you to consider when selecting your aquaponic media.

Media Must Haves

  • Not change the pH of your water – Both initially and over time, the media must not give off anything that changes the pH of the system or contributes any nutrients to the system. Watch out for limestone and marble because they tend to create high pH environments due to their calcium carbonate levels. Diotamite, Maidenwell, and Higrozyme all tend to drive pH down over time. Most river stone and lava rock are inert and pH neutral.
  • Never decompose – Your media should never break down or decompose. If it does, you will be left with both a mess and uncontrollable fluctuations in your pH and nutrient levels. The decomposition process may also leach tannins into your water that could turn it dark and make it hard for you to see your fish. This eliminates the use of soil, peat moss, wood chips, or coconut coir.
  • Be the proper size – Just like Goldilocks, you need to find media that is not too small, and not too big, but is just right. Media that is too small – for example sand, pearlite and vermiculite – will quickly become too compact and not allow good air and water circulation around the root zones of your plants. Media that is too big – for example, large lava rocks – will create large air pockets where the plant roots won’t comfortably establish themselves. The ‘just right’ size for aquaponic media is about 1/2″ to 3/4″ (or 15mm – 20mm) in diameter.

Media Nice to Haves

  • Porosity – The more surface area you give bacteria to establish itself, the more robust and productive your system will be. Plus porous material holds air and water better than non-porous material, and it’s lighter weight. Properly sized lava rock is a great example of this.
  • Be Easy to Handle – Sharp edges are tough on plant roots and a gardener’s hands. If you fill your bed with a rounded or smooth surface media, such as river rock or manufactured expanded clay balls, such as Hydroton, you will thank yourself again and again.

No matter what media you choose, it must also fit within your budget. Because flood and drain aquaponics grow beds are best at 12″ deep, the required media can be a real budget buster if you aren’t careful.

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