Continued from page 4

Cyanobacteria Part 3

It has always been assumed that blue-green algae relied for the most part, if not completely, on photosynthesis for growth and reproduction. This may have been the case up to a few years ago but recent findings have demonstrated that Cyanobacteria do not rely solely on CO2 fixation but can and will thrive in environments that are rich in organic matter (I have indicated this in many of my writings and have always suggested that to eradicate blue-greens one needs to skim more efficiently and/or use a compound that oxidizes organic material out of the water so this food source is no longer present). These findings are confirmed by researchers such as Carr and Whitton, Fog, Stuart and Fay, and others still.

Not all Cyanos can utilize this mode of food uptake as some are Obligate Photoautotrophs (meaning they rely totally on photosynthesis for food and growth). It turns out that most of the ones that fit in this category are freshwater types. Most saltwater cyanos rely on either organic foodstuff uptake and/or on photosynthesis (and are called Facultatively Photoheterotrophs), and will uptake organic food and substances if they are available.

Of course, we all know that our aquariums are laden with organic material. This is especially so if the skimmer we are using is not removing organic material efficiently or cannot remove all or the majority of it because it is either too small, or the tank is so heavily stocked that the skimmer cannot keep up with the amount of organic material produced on a continuous basis. Overfeeding would obviously contribute to this situation even more.

It should be noted also that "light" actually enhances the uptake of organic material (Fay). The situation this puts hobbyists in is that not only are we faced with blue-greens that feed on organic substance and their breakdown components, but that light increases the uptake of these substances and results in a more dense and more widespread growth of cyanobacteria. Sort of a Catch 22 situation, unless we realize that we need to do what ever is in our power to keep the amount of organics in the water low, as low as possible. This requires the use of real efficient skimming (hobbyists who do so, do not generally report problems with outbreaks of Cyanos).

What we definitely need to remember from this is that the combination of running high intensity lighting and not paying attention to the amount of organic material in the tank will definitely lead to the appearance of blue-green algae, as should be evident from the information given above. Two methods need to be used in my opinion:

• Skim as efficiently as you can.
• Remove organic material from the aquarium by using an oxidizer (for instance potassium permanganate solutions such as Redox +).

Excellent skimmers abound nowadays. As a rule of thumb it is a good idea to buy one that is rated for at least twice the size of your tank and to acquire a venturi type. Remember that for venturi skimmers to run well they need to be operated with pumps that can develop a lot of pressure on the venturi valve (this allows it to pull in more air and produce smaller bubbles which results in more efficient skimming). In addition to running such a skimmer, you may wish to add potassium permanaganate in small amounts a few times a week. If you wish to read up on Redox + which is such a product you can go to our SW Library and under Product related articles read the product description. Note that other companies manufacture such products and that you are "not" limited to ours.

One way to determine whether your organic load is high is to perform a DO and a BOD test (dissolved oxygen and biological oxygen demand). This is done in the following manner:

• Take two samples of water.
• Use one for immediate testing
• Store the other in the dark making sure there is no air trapped in the container you use (fill it under water and then put the cap on).
• Test the first sample for dissolved oxygen and write the result down
• Store the second sample for 48 hours
• After that time has elapsed, perform a dissolved oxygen test on the second sample.
• Write down the result
• Compare the results of the first test to the second one and note what the difference is
• If it is greater than 1 mg/l your organic load is high and you definitely need to intervene. This is done either by upgrading the skimmer or making it more efficient, or starting a potassium permanganate solution treatment. Ideally and in most cases the better method is to do both.
• Note that even though the tests reveal to some extent what the DOC (dissolved organic carbon) level is, any protein material that is in the tank that has not decomposed yet is not measured by this test and will eventually increase the amount of DOC even further.
• It is important for correct DO and BOD measuring that your test be chemically active. Most tests have expiration dates listed on the box they come in. Make sure yours is still within the useable period. If it is not you will get meaningless results.

It should be quite obvious from the above that keeping organic loads to a minimum is paramount to avoiding outbreaks of Cyanobacteria. The techniques to do so have been outlined. I suggest you seriously consider using them. I have personally found that adding potassium permanganate several times a week will keep all blue-greens out of the tank. Of course, efficient skimming is necessary as well.

If you now have blue-greens in the tank and need to eradicate them, the methods described above will work for you. In addition to them you should siphon as many of the existing ones out. This prevents them from dying off in the tank, decomposing and adding more nutrients to the water which will make more cyanos grow.

Having a blue-green free tank is not difficult. If you follow what was described here and in the previous two installments you will have no trouble achieving this.

Additional reading:

• Adams and Carr, (1981), The developmental biology of Cyanobacteria, CRC 9, 45-100
• Carr and Whitton, (1982), The Biology of Cyanobacteria. Blackwell Scientific, 704 pp.
• Fogg, Stewart and Fay, (1973). The Blue-Green Algae. Academic Press.
• Stanier and Cohen-Bazire, (1979). Phototrophic Prokaryotes: The Cyanobacteria. Annual Review of Microbiology: 31, 225-74
• Wolk, (1973). Physiology and Cytological chemistry of Blue-Green Algae. Bacterial reviews: 37, 32-101.

To contact Albert J. Thiel

About Albert J. Thiel

NetPets® Main Page

contact information Main Library Reef Plants/Algae

The Fish Center