Aquatics Unlimited: Articles: Algae 101
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Algae 101

for the week of 12/23/99

Part one of three on the green/brown/red slime/crud/hair that aquarists are forever battling.

Is algae harmful? For the most part, no. It is really more unsightly than it is unhealthy. Algae, like other plants, actually filters a lot of harmful chemicals like ammonia and nitrate from the water, making it healthier for fish. It also acts as a nutritious food source for grazing species. On the other hand, algae can be hazardous to live plants when allowed to grow on the leaves and block light.

Is algae avoidable? Generally not completely. Algae needs a handful of things to survive: carbon dioxide, oxygen, nitrogen, phosphorus, potassium and light. If a tank has all these things, algae will grow; if it's missing even one, it won't. Unfortunately, oxygen is required in a fish tank, and CO2, N, P and K are all products of fish waste. Some algae will likely take hold in every aquarium.

Can algae growth be controlled? Definitely; by reducing the amount of any of the above necessities, algae growth can be slowed. Light is the factor the aquarist has the most control over. If live plants are not used (more on plants in the next installment), reducing the intensity and/or duration of lighting will result in less algae. Likewise, fewer fish and careful feeding will reduce the amounts of N, P and K available.

What about algaecide? Aquarium-safe algaecide is not effective on many types of algae. It may work temporarily, but new algae growth usually springs back quickly after treatment, since algae essentials are still in the tank. Eventually all the susceptible algae dies out and algaecide-resistant strains take over, making further chemical treatment ineffective.


"Tip of the week" appeared regularly in 1999 and 2000.

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