Much more rarely than in the case of the algae previously cited, the spherical ones become a problem. However, once established in the aquarium, they also develop a surprising reproduction potential. They often grow in hardly reachable places, like for example among the branches of the corals, where they are complicate to remove. If the spheres composed of a sole giant cell are pierced or pressed, in this way huge quantities of spores are released which amplify their diffusion. Their mechanical removal through brushing is therefore advisable, only as long as there are fishes that feed on these algae and prefer their young stage. Their strong proliferation occurs more frequently in aquaria where other macro-algae (Caulerpa, calcareous algae) are completely absent.
What to do in case of infestation of spherical algae?
Remove from the aquarium the rocks most infected by these algae, by brushing them in a recipient full of marine water. This is well combinable with a partial change of water.
Nutritional competition through the creeping algae
One of the most important factors in the fight against the spherical algae is the nutritional competition. Introduce in a free area of the aquarium some Caulerpa and provide them with the adequate conditions of growth.
If in your aquarium you breed alga-eating fishes, the Caulerpa are usually difficult to cultivate. In this case, you should introduce fishes of the genus Siganus (e.g. Siganus Vulpinus), or Naso (e.g. Naso lituratus), since they both feed on spherical algae.
The Diatoms, also called siliceous algae, make their appearance in any aquarium newly set up in the form of subtle and brown coverings. Some strata of diatoms may also reach thicknesses of a few millimetres, and without the help of a microscope they are difficult to distinguish from the cyanobacteria. The majority of the species only multiply until the content of silicic acid (SiO2), from which they obtain their envelope, is sufficiently high. As soon as this has remarkably decreased, the diatoms are reduced to small remains. Sometimes the tap water can however be very rich in silicic acid (over 1 mg/l). If this water is used as a refill of the evaporated one, this substance is able to accumulate, especially in open aquaria with a strong evaporation. The main problem of an excessive propagation of these algae consists in the significant production of oxygen that may damage the corals. In addition, the siliceous algae represent the food basis for some planarians (Turbellaria), so that in case of an excessive development if these algae, the multiplication of the parasites can as well be promoted.
What to do in case of siliceous algae?
If a massive proliferation of siliceous algae occurred, it would be appropriate to proceed with their removal, sucking them during the partial change of water. The non-fixed rocks, as described previously, can be treated outside the aquarium. Release especially the corals from these algae.
Use the osmosis water for the replacements of the evaporated one. However, even through these plants the silicic acid is not completely eliminated. If the diatoms do not disappear, an ion exchanger (total demineralisation), which will hold the residue of the siliceous substance, may result as useful.
Eaters of the algal substratum such as small hermit crabs, sea urchins and alga-eating fishes, although not being specialists in case of the siliceous algae, can however provide a significant contribution in their reduction. The surgeon fishes of the genus Ctenochaetus appear to have specialised in grazing on the diatoms.
“The golden algae”, under the order Raphidophycea, make their occasional appearance in the marine aquaria as brownish subtle layers, which cover all the surfaces. Being algae composed of microscopic unicellular organisms without a real bond, they easily allow themselves to be fragmented through fanning and can then be removed with a good mechanical filtering, and through the skimmer. However, due to their extreme reproduction potential, the algal coverings often regenerate even after a few hours. For their propagation, it seems that these flagellants need a lot of iron. Generally, the rate of growth is incremented after any partial change of water, with which this element is restocked. The dramatic development of the golden algae can be better contrasted, by decreasing the iron content in the aquarium water. Avoid, in case of an algal flowering of this kind, the partial changes of water and the dosage of any solution of trace elements containing iron. Introduce some rapidly growing algae like the species of Caulerpa. These algae with creeping development generate an effective competition, also because it seems they need less iron than the golden ones.