Denitrification.

esoxlucius

Redtail Catfish
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Dec 30, 2015
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Firstly, I know this has been done to death and I know it'll never replace good old fashion water changes, but the tinkerer in me wants to set up a very very basic system that I can maybe achieve a little success in slowing down the build up of nitrate. I've picked through lots of threads on the forum but they seem to get a little heavy and quite technical. Does it need to be this way?

My basic understanding is that the bacteria you need can only do their job with no oxygen present so you're up against it from the start in an oxygen rich aquarium. But it can be achieved by literally drip feeding nitrate rich aquarium water through a very long filtration process which means normal BB use the oxygen in the first part of the process and as the oxygen disappears then the other BB start forming and these turn the nitrate into nitrogen which gases out. This is the second part of the process.

Some guy in one thread I looked through had a very long length of coiled up garden hose. A small % of his display tank water went through the hose. Somewhere on that long long journey, as the oxygen was depleted, the anaerobic bacteria kicked in. So into the hose went nitrate and oxygen rich water and what came out the other end of the hose was water with no oxygen or nitrate. This is returned to the tank. But the drip drip feed process would mean the amount of water you are ridding of nitrate is negligible.

If my above very basic description is right, and speaking hypothetically, would it be possible to set up a gravity fed system through numerous very long lengths of coiled up hosing so that the drip drip becomes something scaled up considerably.

So basically aquarium water is going through many hundreds of feet of simple hosing and coming out the other end all "clean"?

I believe I have the basics of it but i've no doubt that the simple set up i've described is flawed in many ways. How? Educate me?
 
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jjohnwm

Dovii
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I've read about this type of system many times in the past; the take-away for me has always been the question "Why?"

If you are going to expend the time, effort and money to build this...and devote the space to contain the apparatus...and the goal is to make nitrate-laden aquarium water more like fresh, clean, low-nitrate water...then why not simply devote the time, money and effort into actually changing water? It seems that an automatic water changing system could be built just as easily, and would likely take up much less space.

I get that designing and building something yourself from scratch has its own appeal...believe me, DIY is my middle name!...but for me the appeal is limited when the results don't justify the expenditures.

I'll also throw in a couple of caveats: first, I would be leery of using garden hose for this purpose. When I use garden hose for aquarium water, I make sure that any water that has been sitting in the hose for any length of time is purged rather than allowing it to enter the tanks. Filling or moving water around is fine, the water is in contact with the hose for only a few seconds, but I question the safety of the material from which the hose is made when in contact with the water for long periods. We drank from the hose all the time when I was kid playing outside; if you have ever had a mouthful of water that had been in the hose overnight, I guarantee that you wouldn't put any live fish into it.

And second: the bacteria which reduce nitrate into nitrogen are actually utilizing the oxygen in the nitrate rather than obtaining oxygen from their environment; that's why they can subsist in oxygen-free conditions. But they still require some form of "food", a requirement that some experimenters seem to be satisfying with sugar, vodka or God-knows-what. So add that new set of tubes and gadgets to the equation...and a way to monitor and control the dosage...and...and...you get the idea.

Personally, I'll drink the vodka myself and then just change the water. :)
 

fishdance

Polypterus
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Jan 30, 2007
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I have implemented this with 4mm Low-density polyethylene (LDPE) micro irrigation tube which is black flexible hose as I had several 300m rolls unused. No need to unravel the roll, just join the ends up. Any tubing will do except clear tube to prevent algae growth (oxygenation). There was some improvement in reducing nitrate levels but denitirifcation is a 2 stage process which releases N2O gas and hydrogen sulfide so you need to balance the flow slow enough to deplete oxygen but fast enough to purge gas which creates blockages. I have a dissolved oxygen meter and API nitrate test kit (extremely rough measurements). Overall, I would say only minor improvement but very cheap and easy to implement. I used 600m lengths until I needed the hose back. A wider diameter may be more efficient but more expensive.

There is a bigger focus using aerobic denitrification nowadays. Bio film filters such as K1 go beyond simple nitrification. Deep bed but aerobic is another.

Any steps towards water conservation should be applauded. The next world war will be over water resources as populations and pollution increases. In my case, I go through multiple tonnes of water changes per week as some of my tanks are very big and some of my fish rooms have many tanks.
 

fishdance

Polypterus
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I didn't use gravity fed, but a small water pump or diverted part of water pump will suffice.
As the return water is lacks oxygen, put it through a spare tank or flowing water output to mix first.
 

esoxlucius

Redtail Catfish
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Dec 30, 2015
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I've read about this type of system many times in the past; the take-away for me has always been the question "Why?"

If you are going to expend the time, effort and money to build this...and devote the space to contain the apparatus...and the goal is to make nitrate-laden aquarium water more like fresh, clean, low-nitrate water...then why not simply devote the time, money and effort into actually changing water? It seems that an automatic water changing system could be built just as easily, and would likely take up much less space.

I get that designing and building something yourself from scratch has its own appeal...believe me, DIY is my middle name!...but for me the appeal is limited when the results don't justify the expenditures.

I'll also throw in a couple of caveats: first, I would be leery of using garden hose for this purpose. When I use garden hose for aquarium water, I make sure that any water that has been sitting in the hose for any length of time is purged rather than allowing it to enter the tanks. Filling or moving water around is fine, the water is in contact with the hose for only a few seconds, but I question the safety of the material from which the hose is made when in contact with the water for long periods. We drank from the hose all the time when I was kid playing outside; if you have ever had a mouthful of water that had been in the hose overnight, I guarantee that you wouldn't put any live fish into it.

And second: the bacteria which reduce nitrate into nitrogen are actually utilizing the oxygen in the nitrate rather than obtaining oxygen from their environment; that's why they can subsist in oxygen-free conditions. But they still require some form of "food", a requirement that some experimenters seem to be satisfying with sugar, vodka or God-knows-what. So add that new set of tubes and gadgets to the equation...and a way to monitor and control the dosage...and...and...you get the idea.

Personally, I'll drink the vodka myself and then just change the water. :)
You can't blame me for wanting to have a stab at something like this, after all you're probably a bigger tinkerer than me, lol. But like you said the only reward would be the sense of achievement through building it, the actual nitrate reduction wouldn't be great. And I did read about the vodka dosing and the hydrogen sulphide aspect of the process and the need to balance it all. That's the point where my head started to hurt.

Realistically, for me, it was all hypothetical anyway because i'm just not tech savvy. The hydrogen sulphide bit put me off. My inevitable incompetence would eventually shine through and that stuff would somehow end up in my tank. Too risky for me.
 
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duanes

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There is a school of thought, that putting clay (some use the cheapest, unscented cat litter) as a substrate, below the normal substrate, and in that stagnant anoxic area, it "supposedly" eats nitrate. (no pumps, no coils, no vodka). I have not tried this myself, but watched a video by one of its proponents, it may have even been posted here on MFK..
Years ago (in the late 80s) salt water hobbyists were doing something similar, that I did try, "plenums".
It was to put an anoxic area (plenum) underneath the substrate creating an anoxic area by the non-moving water in the plenum.
I built the plenum, by making a rectangle (slightly smaller than the inner dimensions of the tank) out of 1" PVC, and covering it with untreated garden fabric. Normal PF sand as substrate was put on top, about 3" (the salt water guys were using what they called a "deep sand bed". I did notice a slight reduction in nitrate, but because I keep cichlids (and all dig) each time they'd dig down to the fabric the anoxic area was compromised, allowing enough oxygenated water in thru the fabric to defeat the concept.
The other problem I considered was that although water changes are substantially about reducing nitrate, that's not all they do.
They are important for maintaining alkalinity, reducing hormones the fish exude, supplying base minerals, and a host of other necessary components.
The jungle like look of terrestrial plants growing from the tank that use lots of nitrate, is enough to wets my whistle.
C523053F-D077-4CFD-A9AF-E135DBA66AB3_1_201_a.jpeg
With the use of old fish water for things like plants in the garden, and yard, or flushing toilets, or rinsing toad feces from the patio, I feel sufficiently absolved of being a water hog. At least in my own mind.
5C6548CB-352D-4D8A-9D28-BDE9A2E26B19_1_201_a.jpeg
 
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esoxlucius

Redtail Catfish
MFK Member
Dec 30, 2015
2,041
4,196
154
UK
There is a school of thought, that putting clay (some use the cheapest, unscented cat litter) as a substrate, below the normal substrate, and in that stagnant anoxic area, it "supposedly" eats nitrate. (no pumps, no coils, no vodka). I have not tried this myself, but watched a video by one of its proponents, it may have even been posted here on MFK..
Years ago (in the late 80s) salt water hobbyists were doing something similar, that I did try, "plenums".
It was to put an anoxic area (plenum) underneath the substrate creating an anoxic area by the non-moving water in the plenum.
I built the plenum, by making a rectangle (slightly smaller than the inner dimensions of the tank) out of 1" PVC, and covering it with untreated garden fabric. Normal PF sand as substrate was put on top, about 3" (the salt water guys were using what they called a "deep sand bed". I did notice a slight reduction in nitrate, but because I keep cichlids (and all dig) each time they'd dig down to the fabric the anoxic was compromised, allowing enough oxygenated water in thru the fabric to defeat the concept.
The other problem I considered was that although water changes are substantially about reducing nitrate, that's not all they do.
They are important for maintaining alkalinity, reducing hormones the fish exude, supplying base minerals, and a host of other necessary components.
The jungle like look of terrestrial plants growing from the tank that use lots of nitrate, is enough to wets my whistle.
View attachment 1434157
With the use of old fish water for things like plants in the garden, and yard, or flushing toilets, or rinsing toad feces from the patio, I feel sufficiently absolved of being a water hog. At least in my own mind.
View attachment 1434158
I think the appeal to many hobbyists of nitrate reduction is not that they'll never have to do water changes again, because quite clearly, and as you said, nitrate just plays a bit part in all of this. Because a lot of us have high bio loads it would be nice to stretch out those water changes a bit which a nitrate reduction process would help.

However, i'm not sure the hassle of setting up a system, tweaking it, dialling it in, forever checking it and worrying that hydrogen sulfide could wipe out your stock, i'm not sure all those things on balance are worth it for maybe an extra day before you need to do a water change. As jjohnwm jjohnwm said, just do your water changes or install a drip system.

fishdance fishdance makes a valid point though about future potential water shortages. Water changes and drip systems for what will be regarded as an unimportant niche hobby in the overall scheme of things, will be banned maybe. Then what?

Maybe future monster tanks will have nothing but small shoals of neon tetras in them!
 

fishdance

Polypterus
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Dont be put off by hydrogen sulfide. It's very soluble and easy to off gas.

Have a look at anoxic filters. Low oxygen levels but not anaerobic. This link is a fairly basic explanation.


We can't eliminate water changes but we can reduce them. I recycle old water from breeder tanks to growout tanks but choose very different species to avoid growth inhibiting hormone issues.
 
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TwoTankAmin

Fire Eel
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Oct 2, 2008
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This is an interesting subject and one which I have investigated to some extent.

The first thing to understand is that we all has some denitrification in our tank as long as it is cycled. It is happening in the biofilms where the nitrifying bacteria and a variety of aother bacteria a;; love together. Now this is a microscopic universe. However, the water enters the biofilm and the bacteria closest to this pioint tend to be the ammonia oxidizers. As they take O and ammonia and a few other tings out of the water it moves deeper into the biofilm and the nitrite oxidizers use the nitrite produced by the ammonia bacteria. They also use oxtgen. Yhe water continues its journey through the biofilm where it encounters what are called facultative anaerobes (or aerobes).

These guys are interesting. When free oxygen is present they use that. But if the water reaching them has been depleted of oxygen, they switch to using the nitrate. What is important is that they can live with or without free oxygen so if the nitrate goes via a different path, the facultative bacteria can switch back. There are more ways to process nitrate but these involve continuous anaerobic conditions, special feeding and why bother in most tanks? More cost, ,more equipment etc.

A number of years ago I discovered Hamburg Mattenfilters. These use massive rigid foam filters which are manufactured in a variety of ppi (pores per inch). An example would the the filter in one of my 33 gal. long tanks. The foam is 20 ppi and touches the bottom, front and rear class so there is no bypass, The top of the foam is above the water surface. The foam is 3 inches thick. For a long time it was the sole filter. I did add a small hang-on and a decent sized airstone because the tank is for breeding Hypancstrus plecos and i want to maxiize DO in the water. Thwe hang-on also serves as a way to run things like carbon or crushed coral or anything else I need to get into the water. It is not for nitrification although some might happen there.

My tanks with such Mattenfilters have some of the clearest water in my system. They also have very little nitrate. Why is this the case? Over time the facultative anaerobes colonize the foam just as the nitrifiers and heterotrophic bacteria do. These latter two use oxygen. As the water works it way through the foam, there will be places where the aerobic organisms use up all the free oxygen. By the time the water reaches the facultative anaerobes, the free oxygen is gone and there is now nitrate. And the facultative guys just switch to using that.

There are other benefits to Mattenfilters. My first one took about 3.5 years before I had to remove and clean it. I have another 3 that have not yet been cleaned. I have an Eheim Pro II fitted with the same foam, nothing else. It ran for over 3 years before it needed cleaning.

The absolute best filtration in a tank is a planted substrate. But not all tanks can or will use live plants and some may not use substrate. In such tanks the Mattenfilter is the next best choice, imo. I know a number of scientists who keep fish and who agree with that statement.

For the most part a freshwater aquarium should not need a dedicated anaerobic denitrifying system. These have more application in waste water remediation than most freshwater fish tanks, imo. (I have never done sw tanks which is why I am specifying fw ones here.) If one has nitrate issues, try massive quality controlled media combined with a moderate flow rate.
 
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