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Planktonic Algae in Freshwater Aquariums

Planktonic algae, always present to some degree in freshwater aquariums, are natural inhabitants of every water ecosystem on our planet. In a healthy aquarium, these microscopic, photosynthetic organisms play important roles in converting plant and fish waste into the oxygen and carbohydrates aquatic animals need while also adding visual interest. But in an unhealthy aquarium, algae blooms are clear signs of trouble.

Sources
- Algae can piggyback on new arrivals to your aquarium.
  
  Planktonic algae make their way to a freshwater aquarium in a number of ways. They can arrive with the fish, plants and other objects you introduce from freshwater sources. Even thoroughly dry driftwood collected from a lake shore can harbor algae that will grow in a freshwater aquarium. Algae also can drift into your aquarium through airborne transmission caused by aeration of a nearby pond or by the flow of air between aquariums in your indoor environment. Even if you don't see the algae, they are there.
Types
- Types of algae commonly found in freshwater aquariums are green algae, red algae, diatoms and blue-green algae. A green algae bloom is easy to spot; it turns the water green. Red algae commonly appear as dark spots on aquarium plants and decorations. Diatoms, forms of algae characterized by cell walls made of silica, manifest as a thin, tan coating on aquarium walls, plants and decorations. Blue-green algae, or cyanobacteria, appear as a dark, slimy substance coating plants and decorations toward the bottom of the aquarium and produce a musty, foul odor. Unlike the other algae types, blue-green algae produce a toxin that is harmful to humans and animals.
Nutrients
- Algae need light, carbon dioxide, micronutrients and water. In the freshwater aquarium, light comes from natural or artificial sources and carbon dioxide from fish respiration and decaying plant and animal matter. Some algae thrive on nitrates and other micronutrients present in fish food and plant fertilizer. When excessive light, carbon dioxide and micronutrients are present, algae populations explode.
Management
- Snails can help manage algae populations.
  
  The key to keeping planktonic algae populations under control in the freshwater aquarium is to maintain an environment that limits algae growth. Because algae require light, provide shade inside the aquarium by adding fast-growing aquatic plants. To limit concentrations of the carbon dioxide and micronutrients that fuel algae blooms, keep pump filters clean, avoid overfeeding fish and plants and make regular partial water exchanges. Depending on the fish and plant species inhabiting the aquarium, snails and algae-eating fish can also help limit algae populations.

Animals & Science