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Old 15-10-2004, 05:23 AM
 
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http://www.xs4all.nl/~buddendo/aquarium/redfield.htm

That's a nice tool to use after a water change when you need to work out
how much nitrate and phosphate to add in order to replace the removed
nutrients.

Cheers,

Michi.


Aquatic macrophytes are not marine phytoplankton which is what the
Refield ratio is based on. the avwerage of most submersed plants is
10:1m, not 16:1.
It also wrongly assumes BGA will be caused and cured within pretty
narrow ranges for NO3 and PO4.

I can assure you that I can have a 2ppm of PO4 and 5ppm of NO3 and
never get BGA outbreaks. Likewise I can have a .2ppm of PO4 and a NO3
of 20 and never get any.

BGA will appear if you drop the NO3 levels down very low and slow the
plants uptake(perhaps of NH4 and thereby allowing the BGA an easy
meal, they do not need hardly any N relative to plants)
The reference is also not for FW, but rather phytoplankton. While I
cannot read German/Dutch, I can tell from the names and it appears
that they did not add plants to these experiments, only algae.

They also assume that BGA, in this case Oscillitoria can fix N2 gas
from the air, not true unless they have heterocyst. No heterocyst, no
N2 fixing in this genus. I've never found any heterocyst in dozens of
smaples sent from all over(everyone has this genus)and I also see no
reason for them to be limited EVER in a FW planted tank, their needs
are extremely small relative to the plants and they exist in a
different niche. No hobbyist possesses the needed test procedures or
kits to measure N limitation in this genus, it's in the low ppb range.

Plants are a huge influence in terms of algae and phytoplankton, I
did not see that plants were added in the reference anywhere. That is
a key element if you want to argue this point.

While their "good" range will work, their reasoning has some issues
and the assumptions are large and the observations I've done over the
years don't not show any signs of BGA nor could I ever confirm their
conclusions/observatuions regarding their ratios and BGA
outbreaks/presence.

Add some KNO3 at 1/4 teaspoon per 20 gals 2x a week if you use CO2 or
more depending on lighting/fish load. That alone will keep it away.
See APD for older post about BGA and heterocyst.

Regards,
Tom Barr