- Silicates in tap water and inadequate lighting cause furry patches of brown algae. The organisms responsible for brown algae are called diatoms, and leaving your tank lights on for an extra hour or two each day should rectify the problem. Wipe aquarium glass with a soft cloth and rinse gravel to remove residual specks of diatom organisms.
- The cyanobacteria organism causes a greenish-blue slime coating on everything in your tank. Poor water quality provides all the waste nutrients this algae needs to smother plants and clog your filter. Manual removal is difficult because the slime sticks firmly to everything in an aquarium. Commercial algaecides containing erythromycin phosphate clear up a cyanobacteria outbreak, although some plants may not recover. Ammonia levels increase during and after treatment, so use a water test kit to check for ammonia, nitrate and nitrite.
- Excessive light is responsible for the majority of algae varieties, and spot algae grows during prolonged periods of exposure to bright lights. Hard, vivid green discs growing on aquarium glass are clusters of spot algae. Tackle spots with the abrasive side of an algae scraper tool or scrub it with a rough cloth.
- Gray-green staghorn algae is characterized by an unusual growth pattern. It grows from a single strand into the shape of deer antlers, and drifts at the water's surface, sticking to rocks and tank ornaments.
- Audouinella, or brush algae, is easily identified by its distinct tufts of black fluffy growths on flat leafy plants. Algae-eating fish are particularly keen on this type of algae, or you can eradicate brush algae with a copper-based algaecide in extreme cases.
- Undissolved iron in your fish tank water from an overdose of plant food encourages thread algae. Dark green strings of algae up to 12 inches in length latch onto tank decorations, float freely in the water or grow into your internal filter cage. Scrub the filaments at the base to prevent re-growth, and manually remove all floating debris with a fine net. Carry out partial water changes every two to three days to dilute the excess iron and improve water quality.
- Short, 2-inch-long crops of green algae on your filter and live plants is hair algae. It quickly forms roots in the substrate around plants, and tangles into their root system making removal difficult. Take action as soon as you spot hair algae so that it does not interfere with your aquarium plants.