Do Healthy Plants Release Organics?

dw1305

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Hi all,
Monitoring an aquarium, is about general relative values and a holistic overview, so seeing a gradual increase in TDS will give you an indication that you may have increasing organics. You're unlikely to get a pure increase in non-conductive organics in an aquarium, without an increase in conductive organics also....If your increased water change schedule halts the steady increase in TDS, then you now your intervention was the correct one.
That would be the view I've taken, you can use the BOD concept, conductivity and plant health as a proxy for nutrient status and water quality.

It isn't perfect, but it gives you a framework to work with and doesn't require a lot of expensive equipment or a large input of time.

cheers Darrel
 

jaypeecee

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Hi @Wookii
Sorry if you misunderstood my post, nothing was intended as unfriendly in the slightest way?
OK, I'll pass on your first sentence in post #78 and start again.
...so seeing a gradual increase in TDS will give you an indication that you may have increasing organics.
I don't understand why a gradual increase in electronically-measured 'TDS' has any bearing on organics. I do know that cellulose, for example, is electrically non-conductive. I would need to check the rest. According to Diana Walstad:

"Decomposition of plant residues after one year were found to be 99% for sugars, 90% for hemicellulose, 75% for cellulose, 50% for lignins, 25% for waxes and only 10% for phenolic compounds".

To which we may then add liquid carbon (e.g. glutaraldehyde), chelators, etc. Although this thread set out to target healthy plants, I am guessing that what we are discussing here is equally applicable to decaying plants. It has often been said (by @dw1305) that plants are leaky structures. Indeed, he may have said this earlier in this very thread.

JPC
 

dw1305

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Hi all,
I don't understand why a gradual increase in electronically-measured 'TDS' has any bearing on organics.
It doesn't directly, but polluted (high BOD) water usually has both higher conductivity and ppm TDS (measured by evaporation).

If you add nutrients at least some of the products of their decomposition will be ions, so if you add a protein, it will eventually end up as nitrate (NO3-), via the breakdown of amino acids and the nitrification of ammonia.

You can have <"high conductivity, low TDS water"> like a chalk stream, and low conductivity, high TDS water like a tropical black-water stream, but they both have a low BOD. That is why you need a <"datum value">, for your tap or rain water, before conductivity becomes a useful measurement.

cheers Darrel
 

jaypeecee

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Hi Folks,

I was wondering if it would be possible to try some of the procedures described in the following (they're probably familiar to @dw1305 ):

https://water.custhelp.com/app/answ...ons_-correlation-between-kmno4,-cod,-bod,-doc

Or, what about this:

1 Take sample of aquarium water
2 Insert ORP/Redox probe and note reading when settled (10 minutes or so)
3 Every 10 minutes or so, add a calculated volume of KMnO4* solution or H2O2** solution monitoring ORP for any changes (increase) with each addition. In the case of KMnO4, there may also be a colour change from purple to brown to purple.
4 Note the volume of KMnO4 or H2O2 added when the point is reached at which ORP starts to increase (or colour change with KMnO4)

My thinking is that, when ORP starts to increase, the oxidation/reduction balance will have been reached. And, from this, it may be possible to calculate DOM*** concentration. In principle, can anyone see any errors in my reasoning?

* potassium permanganate
** hydrogen peroxide
*** dissolved organic matter

JPC
 

dw1305

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Hi all,
1 Take sample of aquarium water
2 Insert ORP/Redox probe and note reading when settled (10 minutes or so)
3 Every 10 minutes or so, add a calculated volume of KMnO4* solution or H2O2** solution monitoring ORP for any changes (increase) with each addition. In the case of KMnO4, there may also be a colour change from purple to brown to purple.
4 Note the volume of KMnO4 or H2O2 added when the point is reached at which ORP starts to increase (or colour change with KMnO4)
Yes it is the <"COD method">.

<"Potassium dichromate"> is a better oxidising agent than hydrogen peroxide or potassium permanganate, but it is still of very limited value to us, it really only gives you a "quick and dirty" estimation for very polluted water.

cheers Darrel
 

jaypeecee

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Hi @dw1305
...it really only gives you a "quick and dirty" estimation for very polluted water.
Thanks, Darrel. I appreciate the feedback. What is the reason for this method not being sufficiently sensitive to measure organics in freshwater tanks?

There is a company in Czechoslovakia that produces a freshwater organics aquarium test kit. I'll check it out. I tried the Salifert Organics test kit some time ago but it was a big disappointment. I'll also try to collect my thoughts on why I think this topic is worth pursuing. At the moment, I realize that I'm a lone voice on this.

I've also noticed that the term 'DOM' may be the better one to use as it includes dissolved organic phosphorus, for example. And, fish pheromones.

JPC
 

dw1305

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Hi all,
What is the reason for this method not being sufficiently sensitive to measure organics in freshwater tanks?
It is because COD is a pretty broad brush. The COD is the oxygen demand from all chemically oxidisable organic carbon (C). The oxidising agent (potassium dichromate etc), used in the assessment of COD, burns out all of the organic C, including the component not easily broken down by microbial action. Because of this it tends to underestimate the <"BOD demand"> of ammonia etc.

If you think of the tannin tinted water, it might have low BOD, <"a high biotic index"> and moderate COD. A waste stream with lots of ammonia, but very few particulates, might have a very high BOD, very low Biotic Index and a relatively low COD

Five day BOD is a much more sensitive test, but still less good than a <"Biotic Index">. <"A sonde using tryptophan fluorescence"> gives a better estimation of BOD than COD, but you would still use it with a Biotic Index. The Biotic Index is always going to give you the best estimation of long term water quality in natural waters.

The current Biotic Index for the UK is the <"Whalley, Hawkes, Paisley & Trigg revision to BMWP">.

cheers Darrel
 

dw1305

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Hi all,
I once did a 5-day BOD on a tank. So, that's worth trying, yes?
Yes, we used to do a lot of these, but you really need <"dedicated lab space">.
<"Standard Methods 5210B">. A sample is first analyzed and conditioned to ensure favourable growth conditions for bacteria, which may include adjustment for pH, neutralization of residual chlorine, and/or reduction of DO in supersaturated samples. The sample is then diluted and the appropriate amount of seed bacteria added. The initial dissolved oxygen content is recorded and the sample is then incubated for 5 days at 20°C. After the 5 day period, the sample is removed from the incubator and the final dissolved oxygen reading is taken. BOD is calculated from the DO depletion and volume of sample used following the formula below:

BOD5 = BOD mg/L = [(IDO -DO5) – seed correction] x dilution factor
cheers Darrel
 

jaypeecee

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Hi @dw1305 & Everyone,

Needless to say, the above procedure isn't quite the one I followed! Remember the books of years gone by when the "Beginners' Guide To..." series were popular? Well, I reckon I must have followed the "Beginners' Guide to Biochemical Oxygen Demand testing"! :lol: If I remember rightly, I took a 1 litre sample of aquarium water and measured the DO* content. Then, sealed the 1 litre sample container and put it in a dark place for five days. When time was up, I then re-measured the DO* content. Going by memory, not a ha'porth of difference!

What do you know about Permanganate Value? Is this appropriate for measuring DOM**? Isn't it used by pondkeepers?

For the benefit of anyone who is not familiar with acronyms I've used:

*DO = Dissolved Oxygen
** DOM = Dissolved Organic Matter

JPC
 
Last edited:

dw1305

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Hi all,
What do you know about Permanganate Value?Is this appropriate for measuring DOM**?
It is a less effective than potassium dichromate. Potassium permanganate doesn't as effectively oxidize all the organic compounds in water, limiting its value for determining COD. The main issue with all the COD methods is that they don't oxidise any ammonia into nitrate, so nitrification is not included in the standard COD test, but they do oxidise tannic and humic compounds, which don't really contribute to the BOD .
Isn't it used by pondkeepers?
I think potassium permanganate is still used as a dip for parasites. I was going to say I really hope not as a water treatment, but it probably is, mainly because you could sell permanganate, COD test kit and"sludge busting" bomb.
Needless to say, the above procedure isn't quite the one I followed!
It is really why you need a lab set up for it. You need to culture the microbes, as well as having access to the growth cabinets and reagents. I used to assume that the values we got were fairly accurate, but we were dealing with fairly polluted water.

In cleaner water (and hopefully that includes in every-ones aquarium water) then it still doesn't give you anything like fine enough scale resolution.

cheers Darrel
 
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