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.
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.
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:
I think it's pretty cool that charcoal will remove tannin stains from your water.
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?
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.
Haven't heard an update for awhile, what's the latest with the guru's charcoal system?