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.

[George T]

High PH - Possibly too much potash with the charcoal, early on.  Still lots of evaporation through the charcoal?  It's nice and warm down here - getting ready to plant spring vegetables outside.  Just couldn't resist that bit.

GT
Paul Letby said:

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.  

[Paul Letby]

Very jealous of your weather George!

 

Yes lots of evap through the charcoal.  If I were to do this large scale outdoors I think I would have a layer of gravel over top of the charcoal to keep the water in.  I have worked out for my 80 ish gallon system that I lose almost 5 gallons a week.  The water isn't heated nor exposed to air movement.  I would like to have a fan on the system for the plants, but don't want to see the water usage go up.  Otherwise I think this stuff is great!

[Paul Letby]

Hey guys!  quick update (I know I haven't been here much lately.  That means I haven't had lots of questions!) on what's going on.  You probably already know I had an indoor aphid infestation that I thought I already had under control.  Well... when I had  my back turned with a family matter that took a while it got out of control!  So basically it was so bad I decided to remove all the plants from the bed and throw them outside into the freezing weather.  Too bad, as it was shaping up for a pretty good harvest too.  Lettuce and beets, even a few night scented stalks for fun.  They all grew fine under four 4' fluorescent bulbs. So did the aphids :(  On a side note a few ladybugs that wintered inside the house found them, but couldn't keep up.  Too close quarters to effectively apply soap.

Anyhow, just to add a comment about how the charcoal performed... The roots didn't stick like I thought they would.  Sure, a few pieces did, but it looked to me alot like how hydroton sticks in matted roots.  Just give em a shake and the pieces all fall off.  Neato!

My few redworms I threw into the bed in the fall have multiplied enough for me to find them rather easily too.  Pulled up a few with the roots of the lettuce.

 

So now I wait a bit to kill off the aphids, moved all the houseplants to a different level of the house as far away as I can.

[George T]

That's tough gardening, Paul.  Down here, I have 4-foot tomatoes outside.  Found aphids on peppers yesterday and just knocked them off with water spray.  Hope to get started with aquaponics soon.  

Regards

Paul Letby said:

 You probably already know I had an indoor aphid infestation that I thought I already had under control.  Well... when I had  my back turned with a family matter that took a while it got out of control!  So basically it was so bad I decided to remove all the plants from the bed and throw them outside into the freezing weather.  

[Kobus Jooste]

Paul - try a spray bottle of garlic and canola oil (not much oil - max about 10 - 15 ml in a liter of water) for the aphids.  It does tend to make your hardware a bit mucky, but knocks the aphids out.  Indoors I didn't think aphids would feature though - you germinate your own seeds? 

Paul Letby said:

Hey guys!  quick update (I know I haven't been here much lately.  That means I haven't had lots of questions!) on what's going on.  You probably already know I had an indoor aphid infestation that I thought I already had under control.  Well... when I had  my back turned with a family matter that took a while it got out of control!  So basically it was so bad I decided to remove all the plants from the bed and throw them outside into the freezing weather.  Too bad, as it was shaping up for a pretty good harvest too.  Lettuce and beets, even a few night scented stalks for fun.  They all grew fine under four 4' fluorescent bulbs. So did the aphids  On a side note a few ladybugs that wintered inside the house found them, but couldn't keep up.  Too close quarters to effectively apply soap.

Anyhow, just to add a comment about how the charcoal performed... The roots didn't stick like I thought they would.  Sure, a few pieces did, but it looked to me alot like how hydroton sticks in matted roots.  Just give em a shake and the pieces all fall off.  Neato!

My few redworms I threw into the bed in the fall have multiplied enough for me to find them rather easily too.  Pulled up a few with the roots of the lettuce.

 

So now I wait a bit to kill off the aphids, moved all the houseplants to a different level of the house as far away as I can.

[Paul Letby]

It wouldn't have gotten this bad if I'd been on top of things, but indoors with no predators and an abundant feast aphids were so numerous that the plants were dripping sap, sticky and sickly.  Pretty gruesome. Any plant you cared to touch would rain aphids.  Yuck.

[TCLynx]

yea, if aphids, scale or mites get out of hand indoors, there isn't much left to do sometimes but clean up and start over.

[Paul Letby]

Update on the charcoal media.  After two years it's performed fairly well for a nearly free media.  It has proven to have two major drawbacks however.  One is the fact that it wicks water to the surface where it evaporates and leaves behind minerals on top.  I haven't gotten around to my solution for this which will be to remove the top two inches or so of charcoal and cover with hydroton.  That should completely solve that issue and lower the amount of water I have to add every week. (2 gallons in a 80 gallon system)

Second is the initially high pH.  It has come down as the system aged a bit.  I would imagine if I had rinsed more that it wouldn't have been such a pain.  I haven't tested in forever so I'll have to get around to that and post results.  Still have the same goldfish as were added two years ago.

[Harold Sukhbir]

Hi Paul,

Good news! What about plant growth? and what type of plants are thriving? What about buffering?

[TCLynx]

Other than it not looking good, I don't expect that the mineral stains are actually a problem in and of themselves.

I would be curious about your current system pH.  How hard is your tap water?  If you are getting mineral stains I don't expect that the charcoal was the only cause of an initial high pH though if lots of ashes made it into the system with the charcoal that would elevate pH.

[George]

Thanks for the update Paul.  You've been laying low.  My system PH didn't need any adjustment for months, initially, but it does now.

For those who are ground gardeners, after three years I'm absolutely sold on using charcoal in the ground (biochar, it's known as when used for agricultural purposes).  Actually, it took only about 6 months to be sold on it but it's still working very well - just need to make more of it.  

[Paul Letby]

TCLynx: Tap water isn't hard at all. It's lake water run through Winnipeg's water treatment plant.  I think if I had flushed the system a few times there wouldn't really be much of an issue.  The mineral crystals are hard on the stems of young plants so I'll be removing that top layer and replacing.  Santa provided some cash. :)

pH is around 7.4 right now, lettuce and basil grow very happily.  I have limited light at the moment with one t-12 and one t-5 fixture lighting my little bed, so that's about all that'll grow.