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Re: Seachem questions

On Thu, 24 Dec 1998, Pat Bowerman wrote:

> > 2) Seachem supplies an NPK source in its Flourish, however the levels
> > we set in the product are meant to complement the other natural
> > sources (here I'm referring to P & N) of these elements. If you have
> > even a few fish in your planted tank they should provide sufficient
> > levels of nitrogen and phosphorous.
> I'm surprised that no one took exception to this. A few fish will
> provide all the N and P that I need? And in the proper ratios too?
> Does it matter if my tank is heavily planted, well lighted, and co2
> injected? That statement hasn't been my experience at all. In my co2
> injected, 2w per gallon, planted aquarium, I add nitrates daily and
> they still measure less than 4 ppm.

I understand that Diana Walstad (sp?) ran through this exercise some time
ago. I haven't read that but I have gone through the exercise of
estimating the elemental composition of a staple flake food from the
published nutrient analysis on the label and of an "average cell"
composition, which I think was from a microbiology text. The resulting
composition for the most common 6 elements are:

		Flake	Whole		Average
		Food	Plant*		Cell
	C	48%	43%		49%
	H	7%			6%
	O	34%			28%
	N	9%	1%-3%		13%
	P	1%	0.05%-1%	2%
	S	1%	0.05%-1.5%	2%

* dry-weight basis, per Karen Randall's article on plant nutrition in
Aquarium Frontiers Online, November, 1997.

The electrolytes Ca++, Mg++ and K+ don't appear in my estimated
compositions because they are not major components of biochemicals.
According to Karen's table, K will be 0.3 to 6% of the whole plant, Ca 0.1
to 3.5% and Mg 0.05 to 0.7%.  In the flake food these elements would
probably be part of the "ash" component.

The N:P ratio in this flake food is 9:1 on a weight basis, and about 20:1
on a molecular basis.  Referring to Mark Fisher's info on N:P ratios
favoring different phytoplankton, the N:P ratio in this flake food is
above the 16:1 molecular ratio below which cyanophytes are favored.  This
may not be true for other foods.

Whether or not fish food is a sufficient source of plant macronutrients is
going to depend on a lot of details, including how much you feed, whether
your fish are mature adults or growing young, the amount of light provided
to your tank, the nature of your substrate, the kind of plants you grow
and the composition of your makeup water.  I found long ago that I had to
provide Fe and K in addition to what was available from my fish food and
tap water.  I never saw nitrogen deficiency symptoms while I used the
flake food that I used for the tables above; I'm using a different staple
food now and I do see symptoms of probable nitrogen shortage.

Fish food does provide a lot of macronutrients and it provides them in
ratios that are at least close to the ratios needed by plants.  Whether or
not those ratios are exactly what your tank needs over the long run
depends on a lot of factors that are difficult or impossible to forsee.  
There can be repurcussions to oversupplying macronutrients,
so if I were manufacturing a plant supplement for general use I would not
include large supplies of macronutrients in the mix.  I might sell
separate supplements to provide macronutrients, but I wouldn't put them
into a general use formula.

Roger Miller