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[APD] Re: nutrients

Dave Wrote:

"The "Tom Barr System" (50% weekly water changes plus "reference solution" ferts) makes a lot of sense. It has simplified my
life and seems to be working on my tank (knock on wood...) My question is, what is the mechanism that this system depends on
for success?

The PMDD system described so completely on the Krib uses a nutrient limitation mechanism with three basic components to
eliminate algae:
* Strictly limit phosphate
* Keep traces down to an amount indexed to the Iron level
* Keep Nitrate at 5-10 ppm

The "Tom Barr System" teaches that excess Phosphate is not the problem, nor are excess Iron or traces within the bounds
limited by the 50% water change. What then is the mechanism that allows plants to florish and eliminate algae? It doesn't seem
to be nutrient limitation."

Why should it be?

Seems from what I've read, the research done on tropical shallow lakes with lots of aquatic macrophytes clearly shows(Hoyer et al) that these systems remain macrophyte dominated when enough plant biomass is present, eg 50% or more of the lake substrate/surface area possess macrophytes.
Adding more N or P will favor the plants in such systems.

As far as competition?
Larger plants/algae dominate in more eutrophic systems(richer nutrients) not smaller algae. Smaller algae is adpated for lower nutrient levels. Many research papers reflect this from marine systems to freshwater systems.

As far as competition in natural systems, competition for light is the main adavantage plants have over algae.

With CO2 high light tanks, the best way to keep up with the production of plant growth is to re set the tank. There is very little coupling with bacteria/heterotrophes/fungi/protist and the amount of export in these tanks is very high in the form of plant growth.

With non CO2 tanks, the amount of plant export from pruning is very low, and a much greater coupling with the microbial cycle with the plants.
There is much great regeneration of nutrients in a non CO2 tank, that's why you do not need to fertilize them after an initial break in peroid when the plants are getting established. Small inputs from fish food fertilize the tank's slower growth. Plant pruning and fish food are the in/outputs.

CO2 tanks have far more nutrients added adn far more plants removed.

The recycling of nutrients takes time and CO2 enhaces this beyond the abilities of fish to produce enough waste without high NH4 levels to supply the plants.
The rate of loading into the bacterial cycle is too great to supply the plants with enough nutrients for them to grow well. Thge capacity of the system is exceed and you get NH4 and an algae bloom. Try it yourself by adding more andf more fish to an established healthy tank and feed.

In CO2 enriched tanks, the nutrients run out from fast uptake by the plants and you get what? Algae, it's NOT from too many nutrients, it's from too few.

If you keep adding nutrients and removing the plant growth(keep the plant biomass the same and also the dosing) you will not get algae.

But folks did not test for all the nutrient needs of the plants, one nutrient was removed by plant uptake and the other's appeared high(eg PO4) if the tank as always NO3 poor, the PO4 would build up. Poor test kits contributed.

Similar processes exist in brackish and marine systems.

Tom Barr

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