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[APD] Re: why add PO4 and NO3?

Jared Morris wrote:
> The manager at the LFS I work at has been in the aquarium
> hobby/business for over 20 years, and has had quite a few successful
> long-term planted aquariums (even a marine tank with 20+ species of
> macro algae!).  In his experience, PO4 is plentiful enough (sometime
> too much) in a moderately to heavily fish stocked plant tank with
> regular feeding.  Of course, he has always been a proponent of CO2
> injected, high light (one of his larger tanks once had 6 watts/gal
> halide/VHO!), Fluorite substrate, and heavy fish loads though.

More fish means more nutrients will be input through fish food.  I 
generally keep very light fish loads in my tanks, so I have to dose 
NPK and traces in my high light tanks or the plants suffer.  I don't 
add anything anymore, even traces, to my low light tanks -- I depend 
on the substrate and fish food.  During last night's chat on APC, Tom 
Barr said he also doesn't dose his non-CO2 tanks, so I know I'm in 
good company.

Along with fish load, substrate composition and age can also play a 
significant role in the amount of fertilizer needed IMO and IME.  
Plant selection/mass, tap water composition, the volume and frequency 
of water changes, and light can all have an impact on the amount and 
types of fertilizer needed.  It all comes down to balance.

> I also wonder why, if nitrate is the inevitable end product of the
> (in)famous nitrogen cycle, won't the 5 ppm NO3 we need be produced by
> a moderate fish load, regular feeding, and a good bio-filter?

A healthy biofilter could easily produce more nitrate than is really 
needed.  Again, fish load is important as is the size and efficiency 
of the filter.

> Thanks, I hope I wasn't too long winded or clueless,

Not guilty on both counts. :)  I think you would enjoy Diana 
Walstad's book, _Ecology of the Planted Aquarium_, if you don't 
already own it.  There's a lot of good info there, even for us high 
Chuck Huffine
Knoxville, Tennessee

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