Charcoal as a media

[Paul Letby]

Hey guys, I'm going to open this up for debate, as things are getting a little off topic on my personal system discussion.  There have been questions as to the safety of charcoal as a media, and I'm sure there are questions out there regarding it's environmental impact.  So let's let fly with the questions and hash this out.  I'm definitely not the expert here, and I am hoping George will weigh in on the issues. 

 

Personally I decided to use charcoal based on the fact that I have free access to wood, and needed a cheap and light media for use in a GB supported by a light stand that's not meant to support a lot of weight.  I know that activated charcoal is used in aquaria as a filter media, so I'm pretty sure it's safe.  That said we all know that many things from tropical fishkeeping don't transfer to aquaponics very well.

[Paul Letby]

Finished the GB.  Charcoal is easy to move around and dig in.  Just have to be careful not to break any pieces.  It's not that terribly fragile in the bed because it's so light.  Planted out with some full grown African Violets and seedlings of various types.

Recommend not running water through the bed until after bed is full so charcoal doesn't float.  When it floats at high water level all the little pieces migrate towards the siphon as it drains.  I have to dig up my strainer as it's plugged with little pieces.  Will replace with proper size pieces near the strainer.  Since the charcoal isn't floating now the little pieces ought to stay put.  Charcoal soaking up water very well now, I've added 5 gallons this week to keep level up.

[Paul Letby]

I was browsing Murray Hallam's Practical Aquaponics forum and discovered they're already using charcoal as a growing media.  (Darn it, they beat us again!)  There's one fellow named Daveoponic who's been using it for four years, so we have some long term experience with charcoal as a media.

 

Here's a link:

http://www.aquaponics.net.au/forum/showthread.php?t=687&highlig...

 

I think it's pretty cool that charcoal will remove tannin stains from your water.

 

[Paul Letby]

Today I planted some seeds direct into my GB.  The charcoal has excellent wicking properties; all media is damp.  My max water level is well below the surface of the charcoal, I'm thinking 2-3 inches.  I'm not sure if that's a good thing or a bad thing, but it makes seed starting easy.  Any input on that property?

[Mike Creuzer]

I am thinking that as long as it's getting air down in, it should be OK.

 

In my growbed, I mixed small charcoal bits with gravel. I noticed that the plant roots stick to the charcoal where they drop the pea gravel immediately. Do you see this too? The roots binding to your charcoal?

Paul Letby said:

Today I planted some seeds direct into my GB.  The charcoal has excellent wicking properties; all media is damp.  My max water level is well below the surface of the charcoal, I'm thinking 2-3 inches.  I'm not sure if that's a good thing or a bad thing, but it makes seed starting easy.  Any input on that property?

[TCLynx]

Hum, Strawberries might not like the constant moisture up around their crown if planted into a media that wicks that much but I'm not sure if it would actually be a problem or not.

[Paul Letby]

Just an update on the charcoal as media experiment.  Started a bunch of seeds (lettuce, fernleaf dill, beets and basil) by broadcasting the seeds direct into the GB.  Since the charcoal wicks so well, there were no problems with germination.  I did run into two seedlings that have been hit with damping off.  All others have taken fine.

 

The wicking has created buildup of minerals on upper edges of the top layer of charcoal.  It's kind of grey.  I suppose it could be fungus too, but I have not seen any fruiting bodies.

 

I find this wicking to be excessive and undesirable, so I'm thinking of removing a few inches of charcoal after I harvest this crop and replace with hydroton.  This should keep the top layer dry.  As it stands I'm replacing 2-3 gallons per week in a system holding about 70 gallons.  The water is room temperature.

[Harold Sukhbir]

Hi Paul, just thinking, if the media is wicking that much may be you can adjust your stand pipe a couple of inches lower than is done in the more conventional gravel media. This may help with some of the build-up over top. I tell you, if you stick with it you may find the way to make it go and remember the huge weight benefits involved. Believe me, i know that many people are looking on at this trial with great interest including myself.

[TCLynx]

Interesting about the grey stuff along the edges of the charcoal.  I wonder what it is?  Keep an eye on it for us and a picture might be interesting.

[George T]

Harold's is a good idea for a cheap try at a cure.  It occurred to me that a standpipe could be made of sections of pipe with couplings for easy raising and lowering of fill level.  No glue would be necessary.  Hang in there.  There may be other people using charcoal in conjunction with aquaponics but I've not read of anyone doing what you are.  I too am watching and learning.  You are probably correct that the grey stuff is buildup, a byproduct of the wicking.  The evaporation certainly points to that, as you already know.  I just finished an interesting book "The Biochar Revolution."  It's worth a read for anyone interested in the subject.  I'll read parts of it again for sure.

[Harold Sukhbir]

Hi Paul,

Haven't heard an update for awhile, what's the latest with the guru's charcoal system?

[Paul Letby]

Long time no talk!  I've been busy busy with other things.  Charcoal bed is working well.  First crop of veggies is off to a decent start.  Learning planting densities as I planted too close.  Oh well.  Getting pH closer to 7 and the plants are responding well.  At first they were quite stressed having very little access to iron and other goodies at about pH 8.  Darn aphids just won't completely die and have started repopulating again.  I'll have to post some pics when I get time to show off the funny fuzzies growing on the charcoal.

[Harold Sukhbir]

Welcome back Paul, got a little worried on you going MIA, looking forward to see the pictures.