When I returned Monday morning, I found that the small colonies had grown to coat most of the stones, and glass surfaces of the tank. I responded by wrapping the last glass side of the tank with aluminum foil to limit the amount of light that would be able to enter the system. Upon further research, I found that the Brown Algae, diatoms, is a common resident of newly established tanks.
Unfortunately, one of the leading causes of Brown Algae, as opposed to Green Algae, is insufficient light, not too much light. Oops. Furthermore, Diatoms forms in the presence of high silicates and nitrates. New tanks typically leach silicates from the glass, creating a high ratio of silicon to phosphates.
Diatoms grow well in environments high in nitrates, that may result from over feeding, or a lack of proper filtration. As this relates to Aquaponics, it is important to remember that one of the keys to successfully growing plants, is to have a high concentration of nitrates, therefore, the formation of some diatomic brown algae can be expected.
Brown Algae can be very helpful in an aquaponics system due to that fact that a a pH lower than 7, they will utilize Ammonia and Nitrogen (as nitrates). However, in a pH higher than 7, Ammonia will form Ammonium hydroxide, which is toxic to the algae. If the Brown Algae seems to get out of control, it can be managed by regular cleanings of both the glass, and the objects within the tank. Also, the introduction of certain sucker-mouthed fish, such as plecostomus, will help to manage algae formation.
One of the key dangers of brown algae in an aquaponics system is that it can create blocks inside of the small irrigation hoses used to move water in and out of the grow bed.. As algae continues to form, the relationship between water input and output may become altered to a point where stagnant water will pool at the bottom of the grow-bed. This water can facilitate the growth of bacteria that may be harmful to the plants exposed root systems. Regular maintenance will ensure good flow, and allow fresh water to freely circulate within the grow bed.