Aquaponic Gardening

A Community and Forum For Aquaponic Gardeners

Hello Everyone,

I'm new to the world of aquaponics and have been reading up on it for the past couple of days trying to finds ways to make my aquaponics farm completely sustainable(as everyone else). I've searched and searched and found a couple guys from Georgia who are on youtube who are introducing a very recent rediscovery of using ancient chinese farming methods. They made an "incubator" that acts as a natural pond where the fish can get a somewhat complete source of food(basically duckweed, algae, microorganisms, and worms). If you want to read more of it go to

They also found ways to increase nutrient strengths in aquaponics by adding worm compost tea bags and this biochar stuff to growing medium which supposed is enriched with potassium, magneisum, calcium, and phosphorus.

Anyways they sayed something about using biochar in their medium. I've read up on to make it, how it lowers greenhouse gases, and what it does for plants. I can see how it is great for soil, but there is not much rich information for using it for aquaponics.

Has anyone used Biochar, not charcoal from hardware stores, in their medium? I know it has a high pH and am wondering if someone mixes it with some other medium to lower it. I'm going to use ebb & flow so i'm not worried about water saturation abilities this stuff has.



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Plan to "charge" the biochar with worm castings from the huge worm farm that will be in place to feed the fish

Well I do know people who have used and made natural charcoal for use in aquaponics.  (not charcoal brickettes. but Natural charcoal.)  I don't know how much that is different from bio-char. 


Some challenges with charcoal is that it is light, too light to really hold up heavy big plants. 


It will break down to an extent.


The pH issue will actually be affected by how well it is rinsed (ashes are alkali) but some types of wood charcoal will affect the pH differently than others.  Do some testing before you assume charcoal or bio-char will do what you are expecting.


Aquaponics is a living system so what works in one situation may not work exactly the same way in a different situation.  (Different fish, source water, source wood for the bio-char, etc.)


Remember that the more things you start tinkering with the harder it is to know what has affected the balance of a system.  I would recommend getting a firm understanding of basic aquaponics and the nitrogen cycle before tinkering too much with adding worm tea and the like.  What I mean is make sure the bio-filter is up and running before you go throwing a lot of extra things at it since it will be hard to tell what is going on if you are constantly changing too many things all at once.

Hi Raylard:

I have been using hardwood charcoal from the hardware store since the Fall, in a small aquaponics system in the house.  All I do is break it up into smaller pieces and rinse it.  I am using charcoal instead of gravel as a medium.  I haven't measured the pH so I don't know if it is affecting my system, but I haven't seen any negative signs on the fish (goldfish) or plants (various greens and houseplants).  Unlike what TC said it does not break down, like you'd expect from mulch or other organic matter.  The only way it would break down is from mechanical stress, and even then that would just make it smaller, not make it disappear.  I expected this charcoal to absorb nutrients and maybe true biochar does, but mine seems to be pretty hydrophobic; it will float for weeks.  So I am not sure that charcoal soaks up nutrients like a kind of sponge.  To me it behaves more like a very light gravel medium.  HTH!  Here is a picture of roots in one of my pots, I just reused the charcoal since it didn't break down any.


BTW I agree with everything TC said re:too many variables.


Charcoal break down the way perlite will break down, mechanically definitely.
Try it and see!

Thank you Dave for sharing. Ive been curious about the pH and mixing it with compost, since a lot of people say it shocks plants since the biochar is absorbing itself with nutrients and hindering the plant from do the same. It also increases the production of microorganisms!

The pH of the  Biochar does depends on the material, but also a huge factor is the temperature it was created at. maybe its different materials heat up at different temperatures?

Biochar does decompose, but very very slowly. pretty much neglegible.


I'm going to mix 25% biochar with 50% hydroton and 25% compost to have as my aquaponics medium or in a way to get a neutral pH. I'm very knowledgeable about hydroponics and am using aquaponics and my newly developed vertical growing systems. ( Hopefully adding Tilapia to the mix shouldn't be an issue. I'm definitely going to make sure my biofilter is set up before i take on this next step.


I got all of this info from here and a 1 hour video from stanford on biochar, but its all regarding soil, so...


A simple definition of Biochar is charcoal used for agriculture.  It's carbon.  I make it and use it in soil and have been pleased with the results.


25% compost for aquaponics medium is really out of the ordinary.  I can't imagine that it will drain well.

Yeah i found biochar is basically charcoal but you get the best quality if the wood is fired at a certain temperature. I'm very curious as to how it would to in aquaponics. haven't started yet, been too busy, but when i do i'll be back wiht the results.

I'm think of actually putting the worm castings in a tea bag instead of in the growing medium.

Well a couple members here have done the charcoal thing successfully in aquaponics.


When I start up a new grow bed I like to add a hand full of worms along with some castings into each grow bed just to provide a nice mix of beneficial bacteria to the new bed as well as a starter population of worms to take care of the solids going into the beds once the system gets going.


I think brewing activated worm tea and spraying it on the plants would be a good way to help provide nutrients to struggling plants as well as help combat certain pests and diseases.

Hi Dave,

I'm very interested in knowing what PH you're getting with this biochar medium in your AP. Is it possible for you to test it?

Dave Donley said:

Try it and see!
Interesting. I'll check it out

Hi Harold,

My neighbor makes all our biochar here  in Columbus, NM with pecan hulls which give a char with pH 6.8 -6.9.  He says the pH will vary with the feedstock used.  We can't wait to include our biochar stoves with aquaponics.  

Harold Sukhbir said:

Hi Dave,

I'm very interested in knowing what PH you're getting with this biochar medium in your AP. Is it possible for you to test it?

Dave Donley said:

Try it and see!

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