Brown-Slime Algae

Probably the most common brown algae incurred by aquarists are the brown diatoms. They are usually one of the aquarium's most common and often first colonizers. These algae can be sheet or film-like in appearance, appear as tiny brown dots on the aquarium inside panels, or cover the substrate surface and get quite stringy in appearance where there is sufficient light. Silica/silicate is used in the structure of their cell wall. Depending upon the amount of silicate in solution, their growth can present anything from minor to major labor-intensive cleaning tasks. Besides appearance, when heavily coating objects it can photosynthesize and produce oxygen bubbles, which in severe cases may raise pH to dangerously high levels (above 8.6).

The following may be helpful in the case of moderate growths of diatoms;

Fish: Ctenochaetus hawaiiensis, Ctenochaetus striatus, Ecsenius bicolor, Ophioblennius atlanticus, Salarias fasciatus, Centropyge acanthops, Centropyge argi, Centropyge aurantius, Centropyge bispinosus, Centropyge eibli, Centropyge fisheri, Centropyge flavissima, Centropyge heraldi, Centropyge loricula, Centropyge nox, Centropyge resplendens, Centropyge shepardi, and Centropyge vroliki

Sea Hares: Aplysia californica

Snails: Astraea tectum, Cerithium echinatum, Cerithium muscarium, Nerita albicilla, Puperite pupa, Trochus niloticus, Turbo fluctuosus, Strombus alatus, and Diodora inaequalis

When cleaning brown algae from the aquarium side panels, don't just wipe the viewing surfaces clean by using back-and-forth motion with a cleaning pad. This only distributes the diatoms/silica back into the bulk water where it's used again to produce more diatoms on the surface just cleaned. Instead, place the cleaning pad at the bottom of the surface to be cleaned and slowly slide the pad to the water surface. Then quickly remove the pad and rinse in some clean water. Repeat as necessary. This way, the majority of the diatoms on the viewing surfaces will be "removed" from the aquarium.

As for diatoms on a sand surface, siphon them out if they become mat-like and replace the water removed with freshly prepared seawater. Also, the question sometimes arises why do they keep coming back after cleaning the sand surface. That's because the colonization of nitrifying bacteria in the upper portions of the sandbed in the course of their biological processes produce small amounts of compounds containing silicates. In areas such as the bulk water and sandbed interface, these compounds with the help of light form diatoms, especially during the enhanced activity period associated with re-colonizing the disturbed area. On-going removal of diatom coated sand should be limited to only the upper most grains. Once the bed settles down, which may take a few months, a conspicuous diatom problem should subside.

Tap water, even if processed through an RO system, may still contain silicate. Very few RO units are effective at removing silicate. Even quality RO units remove only about 90% of incoming silicate. To remove all silicate from tap water, one must utilize the proper combinations of resins in well-engineered DI units. Salt mixes should also be tested. Remember, anything that may be composed of silica, e.g., silica sand, Diatomaceous Earth, or decorative rock has a slight solvency at the pH normally found in marine aquariums.

Another type of problematic slime-like brown alga is caused by a dinoflagellate. It can result in large areas, including the surfaces of invertebrates, being coated in a brown gelatinous mass. It is usually introduced on a new piece of live rock or coral animal and can easily become problematic if the bulk water is rich in organic material.

This free-swimming alga is extremely difficult to cure. Silicate is not one of its needs as is the case with diatoms. Unfortunately calcium carbonate is. Bear in mind a small microscope would help identify which form of brown algae is in the aquarium. If the alga cell has a flagellum, i.e., a tail (for propelling itself through water), it is a dinoflagellate. It can be reduced/eliminated with the use of ozone or a UV sterilizer. Also, flowing all aquarium water through a sponge filter, which should be cleaned twice a week, is also helpful. And if a quality brand protein skimmer is not being used, it should be as this pest does best in high organic conditions.