Why Use Charcoal in a Fish Aquarium?

Though not an adequate single filtration method for fish aquariums, a form of charcoal known as activated carbon provides an important cleansing function, removing toxins that can kill or sicken pet fish.

  1. Types of Filtration

    • Of the three main types of aquarium filtration--mechanical, biological and chemical--charcoal performs the chemical variety of water cleansing. By removing harmful chemicals, including chlorine and some heavy metals, charcoal complements mechanical filtration sponges or floss (which remove large particulate matter and waste) and biological filtration ceramic disks or cylinders (which encourage beneficial bacteria growth that consumes harmful ammonia and promotes healthy fish immune system).

    How Charcoal Works

    • The characteristics of charcoal make it serve as a natural sponge, soaking up harmful chemicals and isolating them harmlessly until you remove and clean the carbon or replace it.

    Water Clarity

    • Water particulate matter absorbed by charcoal also contributes to sparkly clear tank water, improving aquarium aesthetics.

    Cleaning and Replacing

    • For all they add to tank filtration, the chemical cleansing properties of charcoal have their limits. Activated carbon wears out over time as it absorbs its capacity of chemicals. You can clean charcoal once or twice and return it to the tank, but eventually you must replace it with fresh carbon. Cleaning or replacing activated carbon at least once a month ensures consistent chemical filtration.

    When Not to Use Charcoal

    • The absorbent qualities of charcoal make it a hindrance when attempting to treat infected fish for diseases. Activated carbon absorbs most types of fish medicines, meaning you must remove it whenever treating sick fish. At the end of treatment cycles, introducing charcoal back into the filter helps remove excess pharmaceuticals.