Why you should use river gravel in your aquaponics system even when you want to use expanded clay

A lot of emails from people asking me questions about what grow media I’m using in my aquaponics system. Most of the time I give them the same answer: “It depends.” I imagine the look on their face just before I hit the send button on a two word response. Then I stop and continue writing.

There are two types of grow media I use in my systems: River gravel and expanded clay. We’re going to talk about why I tend to use river in most of my systems and the benefits and drawbacks of this type of media.

Cost savings by buying in bulk

3/4 inch river gravel

Photo by The Melvin Mulch Company

When we get down to it, river gravel is cheap. Just drive a pickup to your local landscaping business and see what they have. Prices will vary from place to place but usually you can get a small truck load for much cheaper than buying other media in bags. Buying in bulk is another way you can get away with this so cheap. The fact that river gravel is plentiful and you can buy it by the truckload is certainly a pro in my book.

What size river gravel do you need to use?

We need to consider the size of the media that we’re going to use in our systems. ¾ inch river gravel is about the best size I’ve found. It’s large enough that it will hold up plants but small enough that you can work it by hand. That being said, it’s not easy by any means. We are dealing with rocks and when you have thousands of rocks in a pile, it’s going to get heavy.

River gravel is porous

There are a few reasons we need proper grow media. We need something the plants can grow in and develop a root structure. We need the material to be pouros. The gravel has minute spaces on the surface which allow the bacteria to cling to and grow. This bacteria as you know, is what makes aquaponics possible.

pH of your aquaponics system

We also need to consider the pH of our systems. The rivers flowing waters washed away any lime or soft material that might have been in the gravel. This means we don’t really need to worry much about the river gravel changing the pH of our system.

So if you’re trying to figure out what grow media you should use, it’s up to you. River gravel is cheap when buying in bulk.The size of the gravel will matter and ¾ inch seems to be the best when it comes to ease of use and application. We are after a media that will encourage the growth of bacteria and using a porous material like river gravel will do the trick. We also know that over time, waters washed away any trace elements that would have dissolved and changed the pH balance of our aquaponics system.

If you’re just starting out or you’re build a large aquaponics system, try using river gravel inside your grow beds.


If you’re interested in using expanded clay balls in aquaponics, check out my new blog article here.

Categories: blog posts.

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