Re:Ammomium, nitrate, phosphate,algae, plants
Gerard van Klaveren <klaveren at bart_nl> wrote Monday, May 27:
>Subject: ammoniUM, nitrate, phosphate, algae, plants...
>Since some time this stuff is regulary a subject on the APD.
>Is it possible to refine conclusions?
>The questions I have:
> Is it possible the aq. plants do prefer ammoniUM and algae
> do prefer nitrate or even phosphate?
> Or do algae also prefer ammoniUM above nitrates or even phosphates?
>If the first is right, it should be easier to keep the algae out of
>Can someone refine this part of the subject?
There is research that shows that plants take up ammonium more readily than
nitrate, but the difference in preference for the two forms of nitrogen is
not large enough to have practical consequences for us growers of aquatic
plants. Vascular aquatic plants and algae can utilize nitrate very
effectively, lowering the concentration to less than 1 part per million.
The energy necessary to reduce the absorbed nitrate to ammonium is also not
a significant amount in the plant's overall energy budget. Whether the
available nitrogen is ammonium, nitrite, nitrate, or urea, algae and
vascular aquatic plants can take it up efficiently.
All plants need phosphate, and both vascular aquatic plants and algae have
impressive uptake capabilities. They can lower the concentration of
phosphate to less than 1 part per billion.
I am putting in, here, an article published a long time ago in TAG. (TAG
4:2, 47-48 Mar/Apr. 1991). The observations discussed below indicate that
both green water algae and a vascular aquatic plant (Elodea) are about
equally matched in their ability to take nitrates and probably other
nutrients out of the water. I think the last paragraphs about the
disappearance of the green water was not in the original article.
Some Observations on Green Water
It is commonly believed that green water in the aquarium is a
symptom of too great a quantity of nutrients in the water, but I have seen
evidence that this is not always the case. I once set up a five gallon
tank with a six inch Elodea plant in a small bowl of soil,two male guppies,
and plenty of light (two 20 watt fluorescent lights). With all that light,
the water turned green in just a week, and soon I could not see through an
inch of it. About a week later, the Elodea plant had struggled up to the
surface, but it did not look very healthy. During the next several weeks
it only grew a little. Both it and the green water were a yellowish green,
sort of like the color of overcooked broccoli. I wondered why the plant
was not growing. Since it was at the surface, it should be getting enough
light. Because the yellow-green color suggested nitrogen deficiency, I
added 50 cc of Hoagland's mineral nutrient solution (1), a rather small
dose, increasing the nitrate concentration by only 0.6 parts per million
Within two days, the green water got much greener, almost emerald
green. The plant also turned greener, and it grew more rapidly. After a
week, however, everything had gone back to a yellowish green, and the plant
had stopped growing again, So, I added another 50 cc of Hoagland's. Again
things got bright green, and the plant grew some more. Again, the tank
soon ran out of nutrients, and again it turned bright green with more
growth by the plant when the third 50 cc installment of Hoagland's was
What was happening seemed clear to me. Once the green water was
established, the tank became low in nitrogen and possibly other nutrients,
and both the Elodea and the single celled algae became deficient. The
plant was not able to extract enough nutrients to grow very much, and it
clearly could not extract enough nutrients to "out compete" the algae so
thoroughly as to make the algae go away. When the small amount of
Hoagland's solution was added, both the plant and the algae got a share of
the nutrients, and greened up, but only for a while. Soon they had run
These observations suggest that the tank was deficient in nitrogen
except immediately after adding the small dose of Hoaglands. More
recently, I tested the water of another tank for nitrate, a 55 gallon, that
had platys and guppies, two 40 watt fluorescent lights, and thick green
water which had not been changed for six months. The test (with a Hatch
Kit) indicated that nitrate nitrogen was less than 1 part per million, even
though the fish had been there for six months and had been fed twice a day.
It would appear that algae can soak up a lot of nutrients, and, instead of
being over supplied with nutrients, as the aquarium books suggest, a tank
with green water is more often low in nutrients, at least in nitrogen, and
it is the lack of nitrogen, and possibly other nutrients, that accounts for
the commonly observed poor growth of plants in tanks with plenty of light
and green water.
About the fourth or fifth time I added Hoagland's, an interesting
thing happened. The tank cleared up. It didn't happen immediately, but
over a period of about two weeks. By this time the Elodea had grown enough
to occupy most of the surface of the tank. The algae gradually thinned
out, and soon the water was clear. I don't think that the algae was simply
shaded out, because it seemed that quite a lot of light was still getting
past the Elodea to the bottom of the tank. It seems to me that the
disappearance of the algae relates more to the amount of plant in the tank,
rather than to any lack of nutrients or light. Once the green water had
gone away, further small additions of Hoagland's to the tank stimulated the
Elodea to grow, but did not stimulate any regrowth of algae.
One possible explanation for the disappearance of the algae is that
little filter-feeding animals such as rotifers and Vorticella live on the
surface of the plant, consuming planktonic algae. As the plant grows, the
amount of surface area of the plant increases, allowing the population of
these animals to increase until they finally clear the water of algae.
This is only one possible hypothesis, and I am sure there are plenty of
---------- Footnotes ----------
Hoagland's Solution (per liter of stock solution):
1 molar Ca(NO3)2--------------5 ml
1 molar KNO3------------------5 ml
1 molar MgS04-----------------2 ml
1 molar KH2PO4----------------1 ml
Paul Krombholz Tougaloo College, Tougaloo, MS 39174
In hot, humid, dry Mississippi