Ultraviolet Sterilizers

Saltwater aquariums, especially well-lit ones, often fill up with phytoplankton, i.e. free-floating algae. While some phytoplankton is beneficial it forms the primary food for many marine creatures too much reduces water clarity. An excess of phytoplankton may also reduce oxygen levels as the organisms die and decay.

Chemical control is pretty much out of the question for aquariums, as what kills algae can also harm everything else. UV sterilizers, however, effectively reduce phytoplankton populations without endangering your fish and invertebrates. They can also be used to treat certain types of bacteria and parasites.


Aquarium Ultraviolet sterilizer

How UV Sterilizers Work

UV sterilizers work by pumping the tank water past a light bulb which emits enough rays at the UV end of the spectrum to damage microorganisms, shortening their lifespan if not killing them outright.

How effectively the sterilizer does this depends on the strength of the bulb and the dwell time how long a certain amount of water is irradiated. Stronger bulbs and longer dwell times treat a wider range of microorganisms.

How to Use a UV Sterilizer

You need to know the size of your tank before selecting a sterilizer and to decide whether you wish to kill bacteria and parasites or just phytoplankton. The maximum tank size for each wattage should be on the label, as should its purpose. For example, an 8W bulb will kill phytoplankton in tanks of 75 gallons or less. It won't have much effect on other organisms or in larger tanks. Keeping the device clean helps ensure its efficiency.


Don't have the sterilizer on for so long each day that you destroy all the phytoplankton in your tank. Filter-feeding invertebrates in particular depend upon phytoplankton as a food source. If the issue is primarily water clarity, a moderate level of green algae in the water should be tolerable. Note that a sudden excess of phytoplankton normally indicates an excess of nutrients, which could be lethal to your animals, so conduct nitrate, nitrite and ammonia tests before you do anything else.

UV Sterilizer Manufacturers

  • JBJ
  • Lifegard
  • Coralife
  • UltraLife