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What waste do plants produce?

bridgey_c

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4 Jan 2013
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I am just trying to get my head around what stuff is in my tank water. I understand that when I add the inorganic salts, KNO3 etc, they dissociate and we have all these various ions zapping around our tanks. Plants use these ions for various functions in order to live, so they are being used up and thats why we have EI. Fish produce ammonia, NH4, and that is partially used by the plants but our filters use plenty of O2 molecules to turn this into NO2 and then NO3, which is also dealt with by our plants. Is this NO3 in the same form as our inorganic NO3 salts we add in EI? When I hear people talk of organic waste I am not exactly sure what that is? I know plants produce waste but I can't seem to find what (apart from O2 and CO2).... Have I got carbon compounds floating around?
 

dw1305

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Hi all,
Is this NO3 in the same form as our inorganic NO3 salts we add in EI?
Yes.
I know plants produce waste but I can't seem to find what (apart from O2 and CO2).... Have I got carbon compounds floating around?
Yes.

Plants are very "leaky" structures, and some proteins, lipids, hormones and carbohydrates will be leaking out all the time, from leaves and roots. This is particularly true as senescence of damaged leaves occurs.

This is also where the BOD (Biochemical Oxygen Demand) concept comes in really useful. A dead fish or a fed prawn is going to contain a lot of protein, and that protein (via decomposition or excretion of excess nitrogen if they are eaten) will have a very high BOD. The same applies to a fruit like Mango, or a vegetable like Sweet Potato, that you might feed to Loricariid catfish or a Pacu these will have a lot of available sugars (mono and di-saccharides), that will fuel a bacterial bloom, again using oxygen and giving them a high BOD.

Plant leaves are in the middle in terms of BOD, they contain sugars and starch (from photosynthesis), and the chlorophyll protein itself, but they also contain structural carbohydrates (cellulose etc) that are less easily degraded. If a plant is going to shed a leaf, it removes the proteins and carbohydrates first, which is why the leaf changes colour. If a leaf is damaged, proteins and sugars will leak out and bacterial decomposition will occur.

Wood has the least BOD, it is dead tissue and it has no sugars or proteins, and much of the structure has become lignified. Lignin is degradable, but only by certain organisms, mainly because the amount of energy that you put in is almost as great as the amount of energy that you get out. This means that its BOD is negligible.

cheers Darrel
 

bridgey_c

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4 Jan 2013
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Fantastic, thank you, that filled in a lot of the gaps that make a lot more things make sense. For example why high tech tanks need more water changes.

I think this might also explain why my discus tank needs more water changes than a normal low-tech tank.

I also think there is a market for a planted tank qualification. A few of you on here could put together a very nice syllabus on all aspects of a planted tank that would be educational, enjoyable and possibly profitable too! Get a few investors on board and you're ready to roll. UKPT diplomas by 2014.....
 
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George Farmer

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Sorry for the diversion but...
Wood has the least BOD, it is dead tissue and it has no sugars or proteins, and much of the structure has become lignified. Lignin is degradable, but only by certain organisms, mainly because the amount of energy that you put in is almost as great as the amount of energy that you get out. This means that its BOD is negligible.

cheers Darrel
Hi Darrel,

Can you explain why I get BBA only on my wood? I assumed it was the wood breaking down (it's very soft) and the organic matter feeding the algae.
 

dw1305

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Hi all,
Can you explain why I get BBA only on my wood? I assumed it was the wood breaking down (it's very soft) and the organic matter feeding the algae.
The simple answer is I don't know, but I think organic compounds may be implicated. Our local pet shop has truly horrible levels of fish care, (and presumably tank maintenance), and the BBA growth is so luxurious their tanks look like they are covered in Gorilla "fake fur". Another tank with great BBA is the Piranha tank in the "Princess of Wales Conservatory" at Kew gardens.

It is slow growing, which is why I think you don't tend to get it on leaves, other than plants on plants with persistent leaves like Anubias, Echinodorus, Java Fern etc. where it gets big enough to be visible before the leaf is shed.

I've got BBA on the exposed sponges, but not really on anything else. I assume in my case it is because the Ramshorn snails browse it from any hard surfaces, and presumably if I didn't have them it would slowly cover available surfaces. In the tanks where the water is too soft for Ramshorns, it grows in little scattered tufts. Allegedly it doesn't do very well in very hard water, or in tanks with low levels of dissolved organic carbon (DOC).

Others will tell you it is high or low and fluctuating CO2 levels, combined with high light and/or ammonia and/or lack of NO3, or lamps with high kelvin values, but I'm really none the wiser.

cheers Darrel
 

BigTom

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Others will tell you it is high or low and fluctuating CO2 levels, combined with high light and/or ammonia.

cheers Darrel


The only time I ever had visible BBA (in one of the nanos) was when I was away for 2 months and the surface plants grew really thick and blocked light/stripped nutrients/stifled gas exchange sufficiently for 90% of the plant biomass beneath them to melt. Came home to really luxuriant frogbit with nothing but BBA underneath.
 
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