# Dummy Question #003: What's COD and why should we care?



## niko (Jan 28, 2004)

This post of course is preceded by Dummy Question #002:
http://www.aquaticplantcentral.com/...ummy-question-002-bacteria-turning-waste.html

Here's Dummy Question #003:
*What is COD and why should we care about it?*

Let me state right here, early in the maze, that I have chosen to engage in such an effort consuming exercise because I like to think that I could care less how smart&great I feel in my own eyes. If I wanted to feel smart&great by using the internet I'd probably write a nice re-worded presentation of what I've recently learned from people that know more than me. And follow up with a nice and civilized discussion in which I, niko, would look smart on every step!

If my style of tickling your curiosity annoys you you could, perhaps, engage in many amusing and fun discussions here:
http://www.aquaticplantcentral.com/forumapc/fertilizing

...and here:
http://www.aquaticplantcentral.com/forumapc/algae

Either way you will have fun in some way. And bring clicks (money) to the owners of this site. Everybody wins.

Back to our regular programming! 
*What is COD and why should we care about it?*

--Nikolay


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## Dryn (Sep 6, 2007)

COD is the chemical oxygen demand and is a measure of how much oxygen water can absorb during decomposition - the nitrogen cycle! 

Can you explain this more?


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## niko (Jan 28, 2004)

Oh yes I can! With the help of my Uncle Google and my Auntie Wikipedia I can do pretty much anything.

Auntie says: *"COD...is commonly used to indirectly measure the amount of organic compounds in water."*
Here:
http://en.wikipedia.org/wiki/Chemical_oxygen_demand

And while we are at that look at this too:
http://en.wikipedia.org/wiki/Biochemical_oxygen_demand

Now let's take this a little further - toward what's important to us as cheerful, budding planted tank enthusiasts:

Under every tank pictures in the Japanese Aquajournal (Amano's magazine) they show some water parameters. Oddly enough - not all the parameters we are used to watch for. Maybe they don't know about them, haha! But they certainly show COD every time.

Help me out here - pull an Aquajournal and look at it. Do they show low or high COD value there?

(No AquaJournal at hand? Ok, google your heart away, you will find at least 2 useful links. One is from1999. Japanese have been doing this at least for 10 years now. And here I'm trying to introduce the concept...)

*What would high or low COD value mean?*

--Nikolay


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## Natalia (Sep 15, 2008)

Chemical oxygen demand is how much oxygen is needed to fully oxydize organic junk dssolved in water. It is an indicator of pollution, the higher the value- more polluted the water is. In terms of nitrogen cycle, nitryfying bacteria are aerobic and will die without suffucuent oxygen present. If the COD is high all this junk will deplete oxygen causing nitrifying bacteria to die.

In japanese tanks that I looked at the COD is < 6mg/l. In comparison, in very clean rivers it is 1mg/l, in moderately polluted 5mg/l. So, japanese tanks would fall into clean to moderately polluted category depending on what the exact value is. Better than municipal waste which has COD 600mg/l. That is why they suggest to aerate the tanks at night.

I do not remember seeing any kits that would measuer the COD. Are there any around?


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## niko (Jan 28, 2004)

Thank you for asking about test kits to measure COD.

First of all - *COD does not measure how active the conversion of NH4 to NO3 is. COD only shows how much waste is ready to be converted to NH4. Usually we test for NH4, NO2, NO3. Never for the waste that leads to them!*

ADA, Takashi Amano's company sells a COD test kit. From what I can tell it's available only through a special order from ADG or Aquaforest. You won't find it on their websites.

No other US company sells COD test kits for aquarium use.

You can buy professional grade COD test kits from many places. Prepare to spend money.

The bottom line is - *One of the very important parameters of the state of our aquariums is completely ignored.*

*And even if we find a way to test COD we don't have a very good idea how to go about cleaning our tanks from organic waste!*

Mechanical filtration and water changes would be the first 2 suggestions. Also beautiful and smart people like me may suggest adding different species of snails, dwarf shrimp, and Amano shrimp in an effort to put the organic waste on a break down conveyor belt. Good ideas. Pretty pathetic too.

Here's a funny: 
Afer handling raw meat would you feel ok if you were told "Here, rub your hands with this dry towel. Rub well."

That's where we are in our understanding of some aquarium processes. The Dark Ages. Complete with imposing dominant dogmas.

Many of us have learned to run planted tanks by feel, by experience, trial and error. Like jazz musicians that don't know the music notes. It works!

But I hate to see the degree of confusion, frustration, and ton of efforts thrown away that people new to the hobby have to go through. There is knowledge out there that is very, very helpful.

By the way - if you are following my Dummy Question series I have to warn you something: I *will not* spell out clear answers. The reason is simple - if something lands in your lap without any effort from your part you are going to throw it away. Read, look for, ask, find for yourself. I'll just keep trying to make you feel like doing so.

--Nikolay


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## prBrianpr (Nov 18, 2007)

The Organic Compounds can be take out of our tanks simply making water changes, i read that in Aquascapingworld magazines. In my El natural setups I dont make w/c still all are going OK, I think the final product is the nutrients for the plants, so you feed and finally you will have plants biomass


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## niko (Jan 28, 2004)

PrBrianpr,

Water changes do take care of organics. Only part of them though.

To really clean our tanks the best idea we have come up so far is to have a constant slow water change happening 24/7.

Or, as you said - in a tank full of mud on the bottom (El Natural, The Natural, Das Natural...) you can even forget water changes and things will be fine. Somehow.

My point is: We can run a planted tank in many different ways. For the few years I've been interested in aquariums I've seen it pretty much all.

But there are things we should know.

Let's make a good point here:
*A planted tank is a system. Meaning it has different components. It's important to know what they are. It's important to know how they interact.*

Organics apparently are in the very beginning of what causes problems in our tanks. It's wise to get to know them as good as possible.

--Nikolay


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## prBrianpr (Nov 18, 2007)

Well looking the Nature, I can say that El Natural is a kind of natural pond where there create a maybe 70% ecosystem, if you can seal the acuarium and put fish that eats the plants without eating it all you can create a 100% ecosystem.

Thats you say we know the basics of how it works but not all,there are a world of microbiology


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## mudboots (Jun 24, 2009)

And this (the last four posts) leads us back to dummy question 2 on how we care for the uncool bacteria...very interesting topics indeed in these series of questions.


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## niko (Jan 28, 2004)

Mudboots,

Maybe, because you are local, I can tell you some more specific "insider" information.

Actually if you come to our next club meeting I mean to talk about certain 'revolutionary' things. Things that are 'new', 'amazing' and so on. 

In other words - well forgotten old knowledge.

The same things I'm trying to motivate people to find out about.

--Nikolay


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## Zapins (Jul 28, 2004)

And here I was thinking COD = Call Of Duty. A good xbox 360 game


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## niko (Jan 28, 2004)

Zapins,

It is your COD to check out the next thread in this series - *Dummy Question #004*:

http://www.aquaticplantcentral.com/...question-004-what-s-substrate.html#post514075

Let me see if I was right by saying you have learned a lot about the hobby since I first talked to you and that now I can ask you things!

--Nikolay


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## nfrank (Jan 29, 2005)

Niko, this is a great series of questions.

COD tells you how much organic waste there is in the water. While a COD test may be helpful, one can reduce COD by reducing reducing organic waste -- by changing water and cleaning filters.

I pose the related question: *Why is organic waste "bad" and why clean filters to reduce it?*

Part of the answer has to do with aerobic, anaerobic and bacteria-related processes in the aquarium. Also, the color of water (aethethics) and blue light absorption.

Another part has to do with dissolved O2 to support fish and bacteria. For example, when the O2 levels get too low, fish gulp for air.

*But, how are COD and O2 levels related to healthy plants and minimal algae?*

If organics are consuming O2, the O2 levels decrease. To see pearling, the water has to be saturated. Some people like the looks of pearling. Is it also an important indicator? In other words, is pearling and saturated O2 important for other reasons?

I have always felt that algae do not like saturated O2 conditions.... or is it that they dont like the conditions that lead to saturated O2 

I will give others a chance to join the discussion.
--Neil


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## niko (Jan 28, 2004)

It's very obvious that the Dummy Questions are not meant to give specific answers. They are meant to give a perspective. If you see the perspective you will probably want to and could find the specifics.

It's important to know that there is a factor in our tanks that we (if we are aware of) don't really know how to care about, and moreover - many of us don't even know it exists. After this thread more people will be aware about organics. 

ADA does not do anyting out of the ordinary about organics. There is a decades old filtration method that could probably take care of 99% of the organics in an aquarium. But I don't see ADA doing anything like that. The reason being that their tanks work as a system. They've chosen an optimal filtration that makes sense within the glass boundaries of their system. Most of us happen to filter our tanks in way similar to ADA without knowing it and without the rest of the "ADA equation". It works. But we don't have very good answers to many recurring questions.

My point is to make people see planted tanks the way they should be seen. Not as just a vessel full of water in which you dump fertilizers and change water. Which by the way works very well - EI and PPS - and has taken us where we are now. For good and for bad.

--Nikolay


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