Disturbing algae in the marine aquarium and relevant countermeasures – Part 2

Blue – Green Algae (Cyanobacteria)

The wine-red coverings, known among the aquarists as Blue – Green algae, are not only anti-aesthetic, but they also significantly annoy the aquarium environment, especially for their strong production of oxygen. That is easily observable during the evening hours, when there is a greater occurrence of gas bubbles that accumulate under the strata of algae and are mainly composed of oxygen produced by photosynthesis, which cannot dissolve in the water because the latter is already saturated with this gas. Such eventuality results as damaging for the corals, therefore an attempt should be made to stop the growth of the Blue – Green algae. Like a lot of aquarists know, that is easier said than done, also because the causes that lead to the occurrence of these algae can be different. Among the cyanobacteria there are “forms of pure water”, which presumably make their appearance after the start of a new aquarium, and “forms of dirty water” that mainly occur in older aquaria.

The following factors may facilitate the growth of cyanobacteria:

– high content of phosphates and nitrates in the water

– substances with a toxic effect in the aquarium water, such as the heavy metals in too elevated concentrations or softeners and compounds containing phenols of unsuitable synthetic materials (decorations, tubes, filtering materials, etc.)

– too reduced movement of the water (“dead corners”)

– ionic imbalance through the uncontrolled dosage of minerals

– lamps with a too high tone of red and yellow

– intense skimming and/or addition of ozone (forms of pure water)

– very dirty sea bottom or dirty filter (forms of dirty water)

In the case of the not very loved “Blue - Green” ones, it can be very different micro-algae. To contrast them, at least a rough identification with the microscope is helpful.

In the case of the not very loved “Blue – Green” ones, it can be very different micro-algae. To contrast them, at least a rough identification with the microscope is helpful.

What to do in case of infestation of Blue – Green algae?

Balancing of the importation and exportation of the nutritional substances

Success against the forms of pure water can be achieved by reducing the skimming, the filtering by carbon and the quick mechanical one. Sometimes an increase of the administered food also brings advantages. In the case of the forms of dirty water, action shall be made in a diametrically opposite way.

Cure of the water

For well-balanced aquaria (high presence of symbiotic species, few fishes), a monthly 10% water change has proved to be useful. Test regularly the content of phosphates and nitrates.

Optimising the lighting

Check the lighting plant and, in case, use a different tonality of color (see “filamentous algae”).

Using marine water resistant materials

Take away any dubious material from the circulation of the water. Glass, silicone, hard PVC, calcareous rocks without heavy metals can be considered as safe. Under potential risks are all the synthetic substances, which emanate an unpleasant smell (test with hot tap water), or which do not change in the marine water as time passes (e.g. becoming fragile or fading).

Mechanical contrast

Suck the covering of patinous algae during the partial change of water. In order to operate with ease, the diameter of the employed tube should not be too abundant. With the use of a piece of silicone tube diagonally cut and applied to the ending of the one used for the removal of the water, the Blue – Green algae allow themselves to be removed with more ease. The non-fixed rocks can be removed with caution from the aquarium and brushed in a recipient full of marine water. Release especially the corals from the covering of these algae.

Nutritional competition

The cyanobacteria are also contrastable through an abundant growth of the Caulerpa, which at least reduce their excessive propagation. Since iron promote more the growth of the creeping algae than that of the cyanobacteria, a light dosage of this element can be considered as sensible. The zooxanthellae compete with the cyanobacteria for the use of the inorganic nutrient substances, and it is well known that the patinous algae rarely attack barrier aquaria with a dense population of zooxanthellate invertebrates.


Part 1