Algae and Tropical Fish Tanks
Algae are a primitive form of plant-life that will grow wherever there is water, light and a nutrient source, exactly like the conditions in a fish tank.
It is impossible to prevent the introduction of algal cells into the aquarium, as they will arrive in microscopic form with water, either from the tap, or from the introduction of fish, and can even enter the water airborne from the atmosphere.
A typical aquarium is a perfect environment for algae to grow, as there is plenty of light and plenty of nutrients from fish waste. Under ideal conditions, algae does not normally present a problem and the aquarium will just need a regular wiping of the glass to remove typical algal build-up. There are many conditions however, in which an aquarium may experience an 'algal bloom'. When this happens algae of different types, most commonly hair algae will grow very quickly, becoming unsightly and potentially dangerous to plants and to a lesser extent, fish.
Algae comes in many forms including brown algae (slime algae) which is easily wiped off, hair algae (blanketweed) which is fibrous and will cover plants, brush algae, which occurs as small brown-black tufts and is very difficult to remove, and velvet algae (blue-green algae) which forms a film over the substrate and décor, may release toxins, and has a distinctive smell.
Although excess light may cause algal blooms, it is given an unfair proportion of the blame and algae will in fact bloom at low, medium and high light levels. It is usually a combination of factors that cause an algal bloom.
Before using a chemical treatment to kill algae the following causes should be checked and removed:
Direct sunlight for more than a few hours a day
Phosphate levels above 0.2mg/l
Nitrate levels above 50mg/l
Overfeeding (any food left over after a few minutes qualifies as overfeeding)
Waste matter/debris in the substrate
Excess use of plant fertiliser
Natural methods of removing algae are safer than using chemicals and often more effective so they should be employed first. There are many species that will eat algae and a combination of different species often has the best effect. Providing they mix with your existing stock, the following species are all excellent algae eaters:
Siamese Flying Fox's (not to be confused with flying fox's)
Suckermouth catfish (varied effectiveness)
Fast growing plants will also prevent the growth of algae by out-competing the algae for nutrients but for this to happen, the algal bloom should be under control first.