Dead algae mass composition

Cory · Dec 28, 2015

Im curious when algae dies, or appears dead (white or yellow) how much carbon, nitrogen and phosphorus is in it?

Reason: my ATS has lots of algae growth on the surface of the screen. But when i scrape it after 1 week, the bottom growth appears dead or dying. However po4 on the Hanna reads 000. So im assuming that that dead mass still holds that nitrogen, phosphorus and carbon. True?

zzzdiver · Dec 28, 2015

I would think very little just my opinion

Randy Holmes-Farley · Dec 28, 2015

The composition of typical macroalgae is given here:

http://web.archive.org/web/20040720...482/Kaneohe Bay algae N-P Larned Mar Biol.pdf

and some of my calculations from it:

http://www.reefedition.com/phosphate-in-the-reef-aquarium-by-randy-holmes-farley/

For those interested in knowing how much phosphorus is being exported by macroalgae, this free PDF article in the journalMarine Biology has some important information. It gives the phosphorus and nitrogen content for nine different species of macroalgae, including many that reefkeepers typically maintain. For example, Caulerpa racemosa collected off Hawaii contains about 0.08% phosphorus by dry weight and 5.6% nitrogen. Harvesting 10 grams (dry weight) of this macroalgae from an aquarium would be the equivalent of removing 24 mg of phosphate from the water column. That amount is the equivalent of reducing the phosphate concentration from 0.2 ppm to 0.1 ppm in a 67-gal. aquarium. All of the other species tested gave similar results (plus or minus a factor of two). Interestingly, using the same paper’s nitrogen data, this would also be equivalent to reducing the nitrate content by 2.5 grams, or 10 ppm in that same 67-gal. aquarium.

Cory · Dec 28, 2015

Thanks Randy. Could i assume that dead/dying hair algae simply doesnt have its chlorophyll and that it would retain most of its C,N and P still? Chlorophyl shouldnt contain a major part of hair algaes C,N and P right?

Randy Holmes-Farley · Dec 29, 2015

Cory said:
Thanks Randy. Could i assume that dead/dying hair algae simply doesnt have its chlorophyll and that it would retain most of its C,N and P still? Chlorophyl shouldnt contain a major part of hair algaes C,N and P right?

There's no way the algae is just releasing chlorophyll. The cell membranes have likely broken down when it died, releasing most of its internal concents.

Cory · Dec 29, 2015

Ah ok. I guess the top layer of algae is just really efficient. I guess those internal concents would constitute most of the C,N, and P? Whats the dead stuff mostly? Im guess its carbon.