How to Remove Algae in Freshwater Fish Tanks

The microorganisms that form algae flourish in both freshwater and saltwater. A small amount of algae in a freshwater tank is beneficial, since it provides food for algae-eating fish and invertebrates, but too much clogs up equipment, reduces visibility and reduces oxygen levels. Too much algae is an indication your tank contains too many nutrients. The answer is quite simply to clean the tank. After the tank is clean, maintain lower nutrient levels with weekly water changes.

Things You'll Need

  • Large buckets
  • Replacement filtration media
  • Algae scraper
  • Cleaning brush
  • Gravel cleaner with hose
  • Jug
  • Thermometer
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Instructions

    • 1

      Fill buckets with enough water to replace 1/3 of the water in your tank. For example, if you have a 20-gallon tank, fill buckets with 7 gallons of water. Add another gallon in a separate bucket for rinsing purposes. Leave this water to stand for 24 hours, to allow it to dechlorinate.

    • 2

      Turn off the tank's filtration equipment.

    • 3

      Replace the filtration media in the filter.

    • 4

      Remove rocks and accessories with excessive algae on them. Use a brush to remove the algae, rinse the object under a water facet, then dip it in your rinsing bucket. After the object is clean and rinsed, put it back in the tank.

    • 5

      Scrape excess algae off the sides of the tank.

    • 6

      Put the end of a hose in an empty bucket and shake the gravel cleaner up and down in the tank until water starts flowing through it. Focus on siphoning up the scraped-off algae and any debris in the tank along with the water. Stop when you have removed 1/3 of the water from the tank.

    • 7

      Use the jug to slowly refill the tank with water from the buckets over at least an hour so as not to shock your fish. If you have a heated tank, warm the buckets of water on your stove to the same temperature as your tank and replace the water over a period of two hours. Use a thermometer to ensure the water you add is the same temperature as the water in the tank.