Charging biochar with pond water?

Hi folks,

I have been making some batches of biochar and have a decent quantity that needs activating with nutrients. I also have an ornamental pond/fountain that has rather murky water and some smallish goldfish and plants. Just now I put two and two together... if I ran the pond water through a bed of the biochar I could simultaneously filter the pond water and charge the biochar. "The problem is the solution" and all that jazz.

I've done a quick bit of reading and it looks like in principle this will work - the carbon will lock up nitrates, trap particulates, and provide a surface area for microbes to grow on. If I run water through it for a week then dump it in the veggie beds it should be pretty well charged.

1) Will I kill the fish?
2) Will I take too much out of the pond this way?
3) Will the carbon add anything to the pond that shouldn't be there? (my instinct is not).

My thinking is to use a gravity filter setup, with a small pump pumping water from the pond to the top, and a siphon draining water back from beneath the carbon into the pond.

Anyone done something similar? Am I on the right track?

Hi Michael.

I think that if you take a large sample of your pre-charge biochar (charcoal) and run water through it, and if that water runs clean, there's little to no chance of harming anything in the pond system.

Charcoal is used in aquarium filters, isn't it? That sounds like it would work as a pond filter, but you would be introducing different organisms than those found in healthy soil to the charcoal.

From all I understand of making biochar from charcoal, you want to charge it with the organisms you want in your soil. Perhaps if you topdressed your charcoal filter bed with really healthy compost, and perhaps bubbled oxygen through it from the bottom, you might combine the pond filtration idea with that of an oxygenated compost extract brewing process. Perhaps the aquatic organisms would be eaten by the compost organisms, and the water would be filtered as it bubbled up through an intake beneath the charcoal bed.

-CK

Thanks, sounds about right.

Regarding the organisms in the char - I'm not too concerned about that. Adding biochar is a long term game anyway, all I really care about is making sure there is at least some life in it and some adsorbed nitrogen compounds. If the pond algae breaks down in the soil that just goes to feed the soil.

hau Michael,  Your plan sounds more like creating Terra Preta. I like the idea and your plan very much.

I would only bother with the soaking if I wanted to filter my pond water.
How do you plan to incorporate the char into the soil? This is far more important to know since that should dictate how you might want to "charge" the char.
If you are going to bury it, then you will need to follow Chris' advice and get the char mixed with some really good compost then bury that mix.
If you are just adding the char, you can go ahead with your plan or just bury the char as is.

Redhawk

As long as you do not use low quality pre-biochar, all is good. It is not going to kill fish. By low quality I mean, low temperature products that have oils left.
I used biochar in our garden pond which used to have over 300 Koki at one point (12 cubic meters of water). Since it was over stocked I used to drop bags of biochar to suck/filter excess nutrients and other stuff from water. Like a week later, I changed bags with fresh biochar and used the previous batch in the garden. It does work and as you said problem is the solution. This was all before a sick bastard threw two 5lt bottle of domestos (bleach of sorts) over the fence into the pond. Problems of living in a city...
Couple of things,
Rinse biochar before adding it to pond. Any ash left will change the pH of the water. Fish don't like that.
You don't need to crush biochar if you are going to use it in your pond. Actually don't do that, tiny stuff caused problems in my case - filters pump etc. Bigger pieces are as good as finer material.
You might think "well I am already dropping it into water, let me use it right after rinsing it". Well biochar floats, initially. Collecting those back is not a lovely task. I used to put it into Bags/sacks with couple of rocks and let it sink.
About the impact on the garden, what I observed: 1-2 week pond-biochar is like ice tea while compost-biochar is like beer and urine-biochar is like vodka. I will like to have ice tea in every meal! It has to have something with microorganisms.
Hope it helps!

I think this is a really interesting idea. Algae appears in a pond because an excess of nutrients in the water.  The algae itself is "charged" by the nutrients in the pond / sunlight.

It makes logical sense to me that running the water through a filter (biochar in your case) would result in the algae and its nutrients/organic matter being deposited in the biochar.

Since it was over stocked I used to drop bags of biochar to suck/filter excess nutrients and other stuff from water. Like a week later, I changed bags with fresh biochar and used the previous batch in the garden.

Interesting - I hadn't thought of just throwing bags in. It probably soaks up nutrients, but probably doesn't remove much in the way of particulates? I'd really like to double up with removing some of the fines that are making it murky as well, so a flow through would be preferable.

We have a fountain in the pond already. I can't mess with the plumbing of it, but I think I can see how to make pipe arrangement that simply catches some of the falling water and directs it through a wide pipe full of char. But now that you have mentioned bags I am rethinking yet again. I could easily put a bag or two in the basin of fountain area, so that the falling water just falls on the bag and flows through it... That would be the simplest, and least visually obtrusive as well.

Thanks for the input. I can see some experimenting taking place over the next few weeks!

I have started this experiment today. I had a decent batch of biochar made up last week, which has been sitting in water. I have given it a thorough, thorough washing with the hose, until the wash water ran totally clean. I was concerned about the soluble minerals from all the ash, and that adding them to the pond might do some harm. I half filled a large planter pot with the char, so that as it sits on the bottom of the pond the water level is about level with the char. The whole thing is positioned to catch a portion of the falling water when the fountain is running, which percolates slowly through the char - I think it is maybe processing about 2 litres per minute, which isn't very significant.

I'll let it run for a week and see what difference, if any, is made.

I think this is a good idea.  On a similar note, when I go crabbing, I bring back sea water that the live crabs were in.  After eating the crabs, I have sea water left.  I use that as part of the mix to inoculate the biochar with, once it has been crushed.  I also put in compost, worm "castings", urine, and sometimes some really old rotten wood.  I think it's a good mix.
John S
PDX OR

Hi Michael,
Hope this finds you well.
Just reading this post now.
How has your plan worked, 3yrs in!?
It sounded perfect to me...
Any surprises, over acheivements, bad outcome, advice?
Thanks

Late to seeing this post. I use biochar all the time as a filter media in my fish farm. I put the char in filter bags and throw the bags into my filter. One thing from my research and understanding is char does not hold onto nitrates very well but holds onto ammonia.

Hey Steven, good info. How do you prep your char for filtering? As in, how finely is it ground, how heavily was it rinsed heavily during production, and how long do you think it remains effective in your filter?

PS, fish farm on the prairies? More information SVP.

I toss any wood I intend to use for hugelkulture into my pond to charge with biodiversity and nutrients. It helps to bundle it so it’s easier to pull out. I notice the goldfish in there (from fish deposited by the prop owner’s granddaughter) congregate under the woody debris, presumably for shade, shelter and oxygen. I do intend to setup a biochar and gravel filter-aeration cascade for my pond as well.

Douglas Alpenstock wrote:Hey Steven, good info. How do you prep your char for filtering? As in, how finely is it ground, how heavily was it rinsed heavily during production, and how long do you think it remains effective in your filter?

PS, fish farm on the prairies? More information SVP.

To start I use the retort method to make the char because it gives the best char for my application. I don't grind or crush the char at all. I know I can get a lot more surface area if I do I find that I end up with a lot more dust that I have to wash out before using it. So the first rinse is when I douse the char when it just comes out of the retort. I then place the char on a screen to shake the dust and small particles off while I fill the bags. After that I give a rinse to the char until I see no black running out of the bags. This past winter I also started using the char to help with solids filtration, so as the water makes its way through the settling tank, aquaponics tank, biological filter it then goes through a 5 gallon bucket of char. The char should help filter any remaining ammonia and nitrates and polish off the water before it hits the fish tank. I would say I believe the fish did benefit from the extra filtration but I think my char was actually too course to properly filter out the solids. I use whatever clean wood I can get my hands on but I do have a preference for hardwoods. Softwood makes a much more porous char but can crumble and turn into dust fairly easily while hardwoods don't. I want to keep the water clean not make it into a char soup and irritate the trouts gills.