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 bioponica.org.
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 it...how 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.
I've used the natural "lump" charcoal from big box stores as a filter media for my Koi and goldfish with no negative effects. In many ways it is almost the ideal filter media, and probably a good bed media too, except it is so light. The relatively pure carbon does not ever break down chemically, and the porosity and surface area for beneficial bacteria to colonize is unexcelled by any other material. This is what carbon is famous for, its ability to absorb and adsorb materials onto all that surface area. There are two forms of natural charcoal carbon. "Activated" charcoal, used for filtering in both industry and aquaria is charcoal that has been "cooked" , ie pyrolyzed, to a very high temperature, like over 800 deg F, which completely decomposes all the volatile chemicals in the wood, AND drives them off. Some chemical or physical processes are then added to further increase the usable(absorbative) surface area. It is not hydrophobic, obviously, as it would be a terrible filter media if it were.
Regular lump charcoal is not pyrolyzed to such a high heat, like maybe just 500-700 deg F. Thus it retains some of the volatiles, the wood oils and complex tarry organic compounds produced during pyrolyis, which accounts for the hydrophobic behavior when it is very fresh. Since these organic compounds are very nasty, one might think they would be bad for your fish, but remember, the reason they didn't cook out of the charcoal is because charcoal is very tenacious at holding onto them. Firstly, they are just present small traces, and they don't really wash out of the charcoal very fast. The bacteria that colonize the pores in the charcoal love to eat these organic compounds so eventually the bacteria clean up the charcoal, and it fully wets and saturates with water.
The pH issues are just due to the ash content. Initially, this can be wash out. The ash is mostly potassium, so it should just be a good nutrient, when the pH is adjusted. The ash content of different woods are probably all over the map, and may even vary depending on the soil and climate where the trees grew. The lump charcoal I've gotten is either "Hardwood"; probably mostly oak, and specifically mesquite, some pieces of which were too hard to cut up into smaller pieces. I cut the charcoal up using my professional grade hand pruner, trying to cut the lumps across the original wood grain as much as possible. I tried to cut the pieces into about 3/8 to 1/2 or 3/4 inch pieces.
I've made a lot of charcoal for gardening, probably the equivalent of several large trees worth. I'm a firm believer in its benefits in the ground but haven't used it in aquaponics. Charcoal made at a higher temperature with volatiles driven out would probably work better in aquaponics, as studies have shown that it does in the ground. It would definitely be more porous but would be more brittle too, more likely to break down into small pieces. We did hear a report back that there was a lot of moisture wicking to the surface of the charcoal. Maybe someday I'll try it but gravel seems to be working very well for me right now. Good luck.