Re: Algea bloom + killi-related comment

["Tyrone Genade" <Tgenade at sun_ac.za>]

On 30 Sep 2002, at 12:33, Wright Huntley wrote:
 
> The concept of a "limiting nutrient" was still in vogue at the time of
> the original posting. Newer evidence places more emphasis on rate
> equations, as there apparently is no such thing as a real "limiting
> nutrient" for either algae or higher plants. [There have been some
> articles from Tropica and others on this, recently.]

Oh dear Wright, now you've walked right into my enzyme kinetics 
backyard.

There is no such thing as a 'rate-limiting step". Substrates 
(nutrients) can limit rate as the rate of growth/reaction is 
proportional to the substrate concentration.

Limiting factors in plant and algae growth are:
Iron
CO2
Nitrogen
Phosphate
Mg
Ca
K

Reduce any of these and you will see slower plant/algae growth. But, 
algae are more sensitive to Iron concentrations as they can't access 
the reserves in the planting medium. Both are as sensitive to 
Nitrogen and Phosphate levels except that algae respond faster to it. 
A lack of Mg and/or Calcium is far more damaging to plants than algae 
as they are involved in cellular organization. Remove them entirely 
and you will see both plants and algae suffer.
Potassium is very important to both algae and plants as it is needed 
to stabilize their turgor pressure (prevent them from popping or 
imploding).

Nutrients are limiting factors.

In nature and the aquarium CO2 is far from limiting. Light is 
normally the problem combined with our vigorous aeration that drives 
off the CO2. If you have enough bicarb in the water this problem is 
counterred as the plants can better assimilate it provided the pH is 
high enough.

If we sit down and think for a moment, it isn't difficult to get 
tanks of Vallis without special lighting and CO2 suplementation. Why? 
One plant is like another right? No. Many of the plants we want to 
grow in our tanks (Amazon swords, Ludwigia etc...) are actually bog 
plants which have access to atmospheric CO2. They are not really 
addapted to life fully underwater which is why we have to resort to 
all these unnatural means of cultivation which generates algae in the 
tanks for the simple reason that the tank isn't balanced. Vallis is 
fully aquatic and has adapted ways to deal with that life style. It 
can photosynthesize and assimilate CO2 very effectively under water 
and out compete algae very nicely provied the pH is above 6.

Below a pH of about 6 plants have a rough time taking up nutrients. 
TO take up positively charges salts they exchange hydrogen ions. If 
there pH is low outside the plant cell (i.e. high hydrogen ion 
concentration) then the plant can't make the exchange.

For the same reason water with a low pH is often also free of algae...

> Balanced nutrition, combined with a good daily light cycle, will let
> the plants outdo the algae and suppress it to acceptable (i.e., near
> invisible) levels. Algae needs no dark period to respire and grow,
> while most vascular plants seem to need that regular dark time. Give
> them a break (and a night).

The reason is photorespiration. Essentially the plants' chloroplasts 
get saturated with 'energy' and the electro-chemical gradients 
generated by harvesting the light are overloaded. A dark period is 
needed to allow 'energy' to be converted to to sugars etc... and the 
electo-chemical gradients to re-equilibriate.

You can visibly see when this point is reached. When the plant is 
ready for action the leaves will be horizontal to the plane of light. 
As the day progresses the leaves will re-align vertically, 
perpendicular to the light.

CO2 supply is a factor but it counts in your favour.

The moment the plants reach this point switch off the lights. They 
will continue photosynthesizing for some hours afterwards. They will 
still assimilate CO2. The simple algae (which is far more efficient 
at photosynthesis) will simly stop and switch to using up its energy 
reserves and making CO2. The plants are special in that they can 
'trap' excess CO2. During the dark period the plants will take up 
evey molecule of CO2 they can get their 'hands' on. Plants very 
rarely release CO2 esspecially as it is a limiting nutirient. 

Most land plants don't do this but all aquatic plants do. They belong 
to a group of plants known as CAM plants.
 
> My experience is that overdoing the light intensity (particularly with
> inadequate CO2) is a very quick way to unbalance a tank. Getting it
> back from the unsightly results can be rather tedious.

The idea of CO2 addition is what unbalances a tank. Under normal 
conditions plants will outcompete algae. Mess with the 'normal' and 
you have to mess some more to reach this mythical balance. If you add 
CO2 you will have to fertilize and increase the light. If the algae 
are already there in numbers you will only favour them. They will 
quickly adapt to the new levels of nutrients and keep going.

If you stop the CO2 and fertilization you can pump as much light into 
the tank as you like. The plants will outcompete the algae because 
the plants have access to the substrate reserves of nutrients.

If you watch the tank and see when the plants have had enough light 
and then put them to sleep you will see the algae vanish.

Are you at home all day? Then why let the lights burn all day? Set 
the lights to go on in the morning for several hours and then go off 
again only to come on in the evening again when you are home. YOu 
will starve the algae of nutrients and they will vanish.

When the plants are firmly in control continue as before but less. 
Given only half as much CO2 as you think the plants need and the same 
for the fertilizer. Add enough buffer to keep the pH around 6.5 
(morning pH). During the day the pH should rise to about 7.5 to 8 if 
the plants are doing a good job.

> My near distilled tap water (34ppm tds) was killing my Java moss,
> particularly when I added any salt to raise tds. I corrected this by
> adding "Equilibrium" in tiny amounts (< 1/4tsp/G), and my Java moss
> and Java ferns are both growing nicely, now, with or without salt.

What is this "equilibrium"? It probably has Potassium and Mg in it 
(as your Java moss was dying because of a lack of K to stabilize the 
tugor pressure).

> The astonishing thing is that some fish that were giving me no eggs
> are suddenly pouring them out. 

Hmmm... interesting.

> Not only are K, Ca and Na vital to cell metabolism in plants, I see
> that they have a profound impact on the fish, too. 

Sodium still has no known metabolic function in plants. It does play 
a role in osmotic pressure (an adverse role) which is why K is so 
important.

> Getting the ratios
> right may improve many "difficult" breeding situations. Maybe those
> fish with "0" ppm tds in nature get the essentials through their food.
> (?)

The ratios are very critical. The kidneys are adapted to deal with 
the environment the fish is facing. They can adapt to changes but if 
they are not geneticly gearer to handle major salt loss then it is 
tickets. Getting the right salt balance will reduce the stress on the 
kidneys and allow more energy for other, more fruitful, activities.

The 0 tds species have to get what they need via diet but would be 
happier if the environment was just right. Unfortunatly this would 
probably mean some draatic pH changes etc...

Anyhow, keep well
Tyrone Genade
tgenade at sun_ac.za
http://www.tyronegenade.0catch.com
cell#: 084-3354-977

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