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Re: Cyanobacteria, dissolved organic phosphorus

On Thu, 29 Jun 2000, Zach K wrote:

>     In those, it's stated that dissolved organic phos. is unused by higher 
> plants but may be used by some algae- (paraphrased).  Do we know if 
> cyanobacteria or any of the common aquarium algae are able to?  

I have never read that cyanobacteria can use organic phosphorus.  The
references I read on algal use of organic phosphorus were also not
specific to the alge we see in aquariums, but it was my impression that
the ability was widespread among algaes.

>     If so, might this help to explain the variation of 'phosphate' levels at 
> which people succeed, or don't, in controlling algae?- don't most phosphate 
> test kits measure inorganic phos. (po4 ?) and exclude organic phos. (po3 ?)?  
> If so, then the levels most commonly referred to would then be telling only 
> part of the story.

Organic phosphorus is mostly as PO4 (phosphate), but it differs from
inorganic phosphorus in that organic phosphorus is bound to relatively
large organic molecules, while the inorganic phosphorus is just
accompanied by a proton or two.  I think the test kits all test for
inorganic phosphorus only.

Organic phosphorus could account for some of the variations that are
reported. More important I think is the fact that phosphorus levels aren't
always the growth-controlling factor, and when it isn't the controlling
factor it can reach fairly high levels -- say, 9 or 10 ppm -- without
causing problems.  If it is the controlling factor then problems might
appear at comparatively low phosphate levels -- easily as low as 0.2 ppm.  
Whether or not phosphorus is the controlling factor depends on other
factors in your tank.

Roger Miller