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phoenixshade

09-30-2004, 11:22 PM

Algae Control
by Wil Nusser

It is the bane of every aquaculturist. You have made your aquarium the ideal environment for growing lovely plant specimens. You have a nutrient rich substrate, plenty of full spectrum light, and the right water quality. You are even using CO2 injection. Finally, you added your plant specimens, took a bunch of digital photos, and posted them to all your favorite aquarium sites. But two weeks later, there it is... green threads growing on the leaves of your prize specimens. Before long you find yourself constantly having to remove algae from your plants just to be sure they are getting enough light. You may even go to something as extreme as a bleach dip. But sooner or later you can no longer keep up, and your plants start turning brown, developing holes, and dropping leaves.

Algae is a very common problem in the planted aquarium. The conditions needed for ideal plant growth seem to be exactly the conditions that promote algae growth... and sometimes it seems that the algae is outcompeting your plants for nutrients. How does an aquarist defeat such an ubiquitous foe? The answer lies in an understanding some key differences in how effectively these plants compete for nutrients, particularly phosphate (PO4).

The Role of Phosphates

Most aquarists know that phosphate is a key nutrient for all plants, including algae. Phosphate plays in important role in photosynthesis, specifically in the energy-carrying molecule ATP. It is also an important part of DNA and RNA molecules. Yet we also know that phosphate buffers are supposed to be bad for planted tanks, and indeed many of us have unknowingly used a phosphate buffer, then watched the resulting algae boom and plant decline in dismay.

To understand this, we must first look at how phosphate is used in plants. A plant cell in general goes through a two stage cycle: interphase, during which the cell carries out normal metabolic processes; and mitosis, during which DNA is duplicated and the cell reproduces. Phosphate is more important to a plant during mitosis, when large amounts of phosphate are integrated into the duplicate DNA strands.

Higher plants have a more complex metabolism than algae, and as a result they spend most of their cycle in the interphase. During the interphase, phosphate demands are fairly low, as this nutrient is recycled during photosynthesis: ADP and phosphate (indirectly) absorb light energy and are combined into ATP; the ATP carries this energy to wherever it is needed in the cell; and the ATP is split back into ADP and phosphate, releasing the energy. The ADP and phosphate then use energy from light to again become ATP, and the cycle repeats. Demands for other nutrients (nitrate, for example) are higher during this stage, as this is an important component of proteins and enzymes needed to carry out cell functions.

Algae, on the other hand, does little other than reproduce. It spends a proportionally greater part of its cycle in the phosphate-demanding mitosis stage, reproducing its DNA to create even more phosphate-hungry algae. As a result, the algae gets all the phosphate, leaving the plants with relatively little left over to reproduce its own DNA.

Gaining the Edge

The next question is how to use this knowledge to give your higher plants an edge when it comes to utilizing phosphate. Actually, they already have one huge advantage: specialization. Algae is a single celled plant and must take a "jack-of-all-trades" approach to life processes. Higher plants, on the other hand, as a collection of cells working together, are able to develop cells that have specific functions, and can therefore excel at these. One such function is the uptake of nutrients by root cells. As a result, the higher plants will actually outcompete the algae for nutrients, including phosphate, provided the plant has a demand for this nutrient.

In order to keep the demand for phosphate high enough to prevent algae from overrunning the your tank, you must shorten the time your plants spend in the interphase. This means keeping the supply of interphase nutrients higher: carbon dioxide, potassium, nitrates, magnesium, and iron. Furthermore, it means not adding phosphates at all. Don't worry about the plants having enough; there is more than enough in fish food and waste, and if other nutrients are sufficienly present, your plants will outpace algae in its use.

Blueprint for Success

First, make sure that you are adding absolutely no phosphate to your tank. By keeping phosphates low, you will assure that little is available for algae to use.

You will need to add carbon dioxide injection to your tank, if you don't have it already. The target range for carbon dioxide is between 10 and 20 ppm. (Controlling and estimating CO2 levels will be the subject of a future article.)

Potassium can be provided by many commercially available plant fertilizers. Mixing flourite into the substrate will also provide potassium. You may instead add potassium sulfate (available from garden supply stores) at a rate of 1 teaspoon per 30 gallons (1 g/10 L) with water changes.

Unless you have a very heavily planted tank, nitrate is already present in sufficient quantities, and you won't need to worry about adding more. If you find that nitrate is testing at zero, add a small amount (1 g/40 L) of potassium nitrate (again, from garden supply stores) with water changes.

Magnesium can be added in the form of epsom salts, available at most pharmacies. Make sure that you are using pure epsom salts with no additives. (The only ingredient should be hydrated magnesium sulfate.) Add 1 teaspoon per 10 gallons with water changes (1 g/40 L).

Hopefully, you already have an iron rich substrate. If not, you can add laterite nuggets near the root systems of your plants. Every two or three months, you will need to replenish the iron supply with more laterite.

Finally, add a quality liquid fertilizer containing the same nutrients for the floating plants. If you can find one that provides manganese and boron in addition, so much the better.

Following these guidelines, you will soon have healthy, algae-free planted tanks. Even in an aquarium overrun with algae, you can expect to see rapid results: algae will die back, and plant growth will greatly increase.

Questions or comments on this article to phoenixshade@hotmail.com.