02 testing vs. nutrient status

detlef

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Would the reading of a DO meter reflect the (inorganic) nutrient status in a well planted/running tank like it does with CO2 concentration?

In other words:
Does the amount of a specific nutrient in the water column correlate with O2 production rates similar to CO2 levels (taken aside the slower response time of plants to variations of nutrients vs. CO2)? If so could the DO meter be used to dial in optimal nutrient levels?

Best regards,
Detlef
 

Tom Barr

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At the whole plant level DO is an excellent integration tool.
But not for the individual components.

O2 is the product of growth in general, not any one particular nutrient.
CO2 would give you the best correlation as it's the largest % of plant biomass and most often limiting.

Regards,
Tom Barr
 

detlef

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Well, while I see DO's as an integrational tool for plant growth and related O2 production I was in hope that nutrient differences of high impact on growth such as KNO3 would show up on DO's as well.

It's hard to believe that growth differences of as much as 3 times more for KNO3 ≥20ppm vs. 5ppm as for example found by P. Krompholz would not show up on a DO meter. Probably I'll own one soon and proof for myself that I'm wrong :)

Anyhow, thanks for replying.

Best regards,
Detlef
 

Tom Barr

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Measuring dry weight biomass over time vs a O2 levels are different measures.
Both integrate many factors in growth.

For example some plants high produce high O2 levels while others do not but still produce lots of biomass.

How might that occur?

Think about that for awhile, think about plants that send most of their energy to the root zone.

If you are able to limit something like say KNO3 dosing,but still use K2SO4 and you had everything else in a non limiting concentration............ then it would show pretty well.

Otherwise it'll mainly be general growth/production parameter. You can tease apart some relationships with statistics in natural systems, but sometimes these are not really significant at that level.

The same might be true for plants unless under strong limitations, which generally do not occur in planted tanks for long without some other issue also appearing, folks might do it, but often it's accidental, not purposeful. Fish waste adds a fair amount to prevent such strong limitations for N and P, but not always, a number of folks have strong cases of each.

DO should correlate, I'm not sure how well and you are also going to need to integrate a DO level that rises and falls through time as well, that will change.

The fish load and rotting plant biomass from pruning will also cause issues.
Different plants/species respire and use more/less O2 as well.
Differential photorespiration abilities also vary and will influence things, Hydrilla is excellent for this reason as well as method of CO2 sequestration.

But to compare how well a system is doing in general, especially if pearling is your interest or gas, then DO is excellent.

But teasing it apart into the individual parts takes some doing and care but cane be done.



Regards,
Tom Barr
 

detlef

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What I plan on doing will be solely based upon O2 testing so no dry weight measurements in mind. Thanks for directing me onto the more complex side of things. I'm well aware of the difficulties to arrive at reasonable findings. Thus, I not only have to do lots of testing during a long time (for weeks or even months I suppose) I likely have to limit the results to my very own system also.

But first things first, I have to get a DO.

What are non limiting concentrations for K+, Ca and Mg?

As always I appreciate your input.

Best regards,
Detlef
 

Tom Barr

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Well, here is what you can do:

I think you can use the declines in O2 for things like NO3 PO4, Ca, K+, variation etc and correlate that with growth. You need to be a bit careful with CO2.
It will dramatically affect plant growth so careful precise measurement is required.

Now....if you did a non CO2 method, that would be far less of an issue.
Which is the typical case in most natural systems..........


Regards,
Tom Barr