Excess algal growth is seen by green water and/or a green blanket or hairs on the gravel, glass sides or plant leaves. In new aquaria or where the lighting is low, a brown form will grow. Rarely, a blue or red form is seen. To eliminate algae three conditions of the aquarium must be examined and corrected if necessary.
LIGHTING
Excess lighting will encourage algae, especially if sunlight strikes the tank. Always shade the aquarium from natural light and use artificial lighting, which can be controlled. If real plants are used these require a certain density of light per area of leaf to photosynthesise, hence the same light levels are required whether you have one plant or one hundred. If the real plants are few in number the surplus light grows algae, therefore plant densely or not at all. An aquarium with plastic plants can have lighting just for viewing or even coloured lighting, which will inhibit algal growth.
BALANCE
The ideal aquarium has a biological balance, seen by ice-like clarity to the water with lively, colourful fish. The bacteria in the tank will balance the excreta from the fish providing the water is regularly diluted via partial water changes (about 25% every week or two). If the aquarium is neglected, the dissolved solids from excess food, faeces, plant debris and bacterially produced nitrates will fertilise the algae encouraging rapid growth. In view of the high nitrate content of some tapwater, collected and filtered rainwater is preferable, where possible. FEEDING Surplus food will encourage algal growth, always feed a few flakes to the waiting fish and stop as soon as any are left over, remove the surplus too. Beware of frozen or fresh foods that cloud the water with dissolved or finely dispersed nutrients.
ALGAE TREATMENT
It is no use pouring Algae Cures into a tank full of algae and excess biological matter. The imbalanced tank will just absorb the active ingredients and the algae merely falter and then start re-growing. Scrape off all the algae possible and siphon it out. Ornaments, rocks and plastic plants can be bleached clean (rinse thoroughly!). Do a 25% water change, "hoovering" the gravel with the siphon tube. Then add an algae treatment to prevent re-growth. If you prefer to have algae in the aquarium keep the front glass clear with a cleaning magnet or (soapless) plastic pan scourer. Use lots of light to favour the green over the brown or blue varieties. Algal volume can be controlled with algae-eating fish such as Sucking Loach (Gyrinocheilus aymonieri), Bristle-nosed Catfish (Ancistrus spp) or a Plecostomus (Hypostomus plecostomus). Snails will not help, in fact they will breed until the numbers become a problem.
OTHER IDEAS
Koi-keepers use water soaked over hay to reduce "green water" in ponds. Try this in your aquarium, barley is the best choice. There is no algae in Amazonian acidic waters so check the pH and reduce it (slowly) if too high. Water stored over peat is best.
The Aquarian Advisory Service,
P.O. Box 67, Elland, West Yorkshire HX5 0SJ.