The Q&A Archives: Algae Growth

Question: Algae black and grey in color continues to grow on the rocks of the waterfall and on the sides of the pond. This is not the green form of algae. After a few days the problem starts again. There is an expensive filter system including the system lighting that cleans the water before it's released to the water fall.

The system people of the products and system haven't been able to help us. Any ideas on who to contact or ideas?

Answer: Some smooth algae growth on the sides is considered a sign of good health in a pond. Fish feed on algae.

But too much algae, floating or attached, detracts from your enjoyment, causes large pH fluctuations, and can dramatically reduce oxygen levels at night.

The underlying cause of algae blooms or excess string algae is too much nutrient. Algae is controlled by killing algae cells, removing sunlight, or removing food.

Floating and marginal plants will reduce the amount of sunlight reaching the pond and inhibits algae growth. Covering approximately 60 - 70 percent of the pond surface with floating plants is recommended.

Avoid topping off or replacing pond water with nutrient-rich tap water.

Manually remove string algae with a brush or similar implement. Clean implement with bleach after use. Think of this as harvesting and removing excess nutrients.

Avoid fertilizers designed for land plants as these contain phosphates. Also, avoid liquid fertilizers or use them very carefully, otherwise you will feed the algae. Do not let rainwater runoff from the yard enter the pond. It may be carrying lawn fertilizer.

A non-toxic blue or black aquatic dye may be used to reduce the amount of sunlight entering the pool. However, this will require raising submerged plants more closely to the surface of the pond, and some of the dye is removed with partial water changes.

Hope one or all of the above strategies works!

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