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!

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 aquaponic grow media . Aquaponic Grow Media
Most people use either gravel or expanded clay for their 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 grow media.

Aquaponic Grow 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″ – 3/4″ 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.



  1. Nicolas February 24, 2014 at 9:32 am

    Hello Sylvia,

    I just discover your website and it seems really interesting.

    I do have a question about expanded clay. I have a small system with goldfish in my house with expanded clay growbed installed above my aquarium (200l) with a loop siphon system.

    Since several weeks I have problems decreasing the GH of my water so I ran a few test and I discover that expanded clay are dramatically increasing the GH! I know that too high GH is not excellent for the fish but also that it can reduce the availability of several elements (such as iron) for the plant.
    I wasn’t expecting that at all so I would like to know if you have advice about how to mitigate the impact of clay on water quality?

    Thanks for your reply,


  2. Sylvia February 24, 2014 at 6:59 pm

    Hi Nicolas. Expanded clay media typically doesn’t have much of any gh on its own it defiantly doesn’t have enough to raise some ones gh.

  3. Nicolas February 25, 2014 at 4:14 pm

    Hi Sylvia,

    Thank you for taking the time to answer me.

    I will make the test again and if the results are confirm, I’ll ask the community about it.



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