Backyard Aquaponics
A place to discuss aquaponics

We invited some new friends over to dinner the other night. The man is a research scientist at a nearby center that studies watersheds, and things like water contamination and the dynamics one finds in a creek. It's a very established and well-respected facility. When he saw the AP system, his eyes lit up like a kid in a candy store. He asked non-stop questions for the next half hour, dug about in the gravel, and admired the bio-film, rubbing it between his fingers. Too funny! I explained everything top to bottom, and of course he understood. I was reminded of things I forgot about my own system, and I learned a few things, too.

Steve, your theory about Nitrate off-gassing is almost correct. Nitrate itself won't offgas, but there are additional bacteria in the nitrogen cycle that will transition Nitrate to Nitrous Oxide (N2O - laughing gas) and then more bacteria to go to Nitrogen gas (N2). Who knew! More bacteria!

The reason that gravel with a textured surface is important is that not only does it provide more surface area and homes to bacteria, but it also provides anaerobic micro-environments. He said that these transitions in the nitrogen cycle happen in anaerobic environments. I think surely he means the part of the cycle that begins with Nitrate. I was shocked that not only did I have anaerobic parts in my filter, but that I wanted them!

He wondered about using sand filters in our systems to get a lot of surface area for the volume. At the time he asked, I couldn't recall if anyone used sand, but now that I've had time to think, I do recall mention of a few folks using limited sand for root crops. My thought at the time was that they might clog up with solids.

He loved the expanded clay pellets, and seemed delighted to learn that they were in the bottom half of my grow beds. He was amused by the idea of composting worms in the beds, and thoroughly approved of the crushed coral in there to moderate the pH.

Overall, a very enjoyable evening. It's not too often you get to educate a research scientist, and also not too often you get to pick the brain of one.

Nice one JP.....

So some anaerobic areas are also important to a system, as in nature where you will get some areas that are anaerobic as well as aerobic areas.. So the nay sayers who say gravel beds are bad, they have anaerobic areas in the bed are very bad and lead to toxicities in your system, are half right... Yes there are some areas of anaerobic activity in a gravel bed but it's a good thing....

Is it a "good" thing though?

I'd agree that they are not bad things but from what Janet said the micro anaerobic areas result in the anaerobic bacteria converting nitrate to N2O to N2 which gives it back to the atmosphere. Is that something you want to happen? Wouldn't we want to keep the N in the system for the plants? Or is it just another one of those things that don't really matter and we shouldn't get stressed over?

I'm guessing the later

I'm not going to stress.....

I use sand, not white beach fine sand, but coarse sandbox grade and I find that although it drains slower, It retains water pools between planted mounds where solids coagulate and allows natural current to run through the beds, kind of like a creek bed. I don't have to use grid piping to get solids distributed, the current does it and floats "downstream" settling in eddies and in natural low spots. The biggest disadvantage is preventing algea growth as the pools settle. I keep white board styrofoam over the pools. Suppose I should convert to rafts.

I've got 1/4" to 3/4" gravel for my GB's Maybe I should have gone with the crushed road gravel -- like sharp pea gravel with lots of coarse sand mixed in.

I'm sure I posted this somewhere before.....

Regarding the nitrates gassing off as N20 and N2.... yep shows the whole nitrogen cycle...

That's fantastic Janet and thanks for sharing, I certainly have learnt from the infoe you have passed on

Indeed, thanks VERY much for sharing.

Yep, knew that it was the anerobic bacs that did the final conversion, but you have certainly answered the HOW for me.

Regarding do we want them? I'd say YES. If our systems are very oygenated then they will not be the dominant bacterial species, existing only in the micro environment of deep eithin the pores of the gravel. Everything has its part to play if in the right ratios.

Thanks again! Soooooooooo, when is he washing his gravel, JP? LOL

Great pic, Rupert! I hadn't seen that, and I -thought- I had read the whole forum. hmmmm....better start over at post#1.

I am happy to have my little anaerobic micro-environments. Right now my nitrate is running pretty high. I wonder if shutting down a bed for a day and letting it get stinky would help drive off more nitrate. Hmmm. Nah, not gonna do it. I don't think the fish would like that.

I don't think he's going to start washing gravel just yet, but it won't suprise me if there's a knock on the door -- him and his scientist friends. "Hey, can we come in and play with your gravel? Can we measure the bio-film? Can we get a water sample? Huh, huh, can we huh????"

i have seen that pic before, but didn't use it on the forum becasue i didn't want to confuse the issue. But it DOES present a more complete nitrogen cycle as it happens in nature.

JP, i LOVED the bit where your friend was getting all excited over the bio-film...................oooooohhhhhh yeeeeahhhhhh.......bio-film.................grrrrr.

LOL

Steve, by the sounds of it, you need to get reets to take a week off work and stand in your fish tank to get a biofilm layer on her. Never know where it might lead you!

......

ROFLMAO