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Do I Need a UV Steriliser On My Fish Tank Aquarium

Ultra Violet or UV Steriliser are used fish tank aquariums to help remove unwanted free floating algae, parasites and bacteria from both freshwater and marine aquariums.

A UV (Ultra Violet) light will alter and disrupt the cellular structure of living cells found in algae and bacteria which effectively kills them off by preventing them from reproducing which will effectively remove them from your aquarium system. This is done in quite a simple manner by the UV filter as it will be part of where the water flows in your system and so all water will pass through it as some point. Many people will install these on the inlet to their filter if a sump or canister filter is being used. The system itself has a UV bulb in it which will shine on the water as it passes through.


It is important when choosing a UV steriliser that you get a unit specifically for the flow rate and aquarium size you are installing it on otherwise the available surface area will not be large enough to eradicate the unwanted bacteria and algae. It is also possible to get a canister filter with a UV steriliser built in to it which effectively takes away this concern as the manufacturers have optimised the UV filter size based on the flow rate of the filter it is attached to.

So, to work out whether you need a UV steriliser or not is something which you can normally tell from the visual water quality and fish behaviour.

If you are experiencing any of the following symptoms it might be worthwhile investing in a UV steriliser:

  • Poor water quality – green water
  • Algae blooms
  • Parasite related fish diseases such as Ich
  • Harmful bacteria present in the aquarium

It is more common to install a UV steriliser in a marine tank than a freshwater one, this is down to freshwater planted aquariums taking care of any bacteria or parasite issues and algae blooms by the plants themselves using up all available resources which these things would require to survive. It may be that you are keeping mbuna or other rift valley African cichlids which eat algae and so you want it to grow rather than killing it off.

Also worth noting is that the UV steriliser will not distinguish between beneficial bacteria and harmful bacteria and will kill all types so if you are planning to use a UV steriliser in a marine tank and don’t wish to kill off any of the free floating beneficial planktonic animals like Amphipods and Copepods then you could always put the filter on a timer to only come on when the main lights are on as these beneficial bacteria tend to hide away in rocks during daylight hours. A UV steriliser may also have a negative or neutralising affect treatments you may add to your aquarium so be sure to switch it off if you are treating your fish with any chemicals.

The last thing to note is that a UV steriliser bulb would need to be replaced every 6 months so this is a cost consideration worth taking in to account if you are considering purchasing one. It can potentially be dangerous and should be noted that you must never look at the UV steriliser bulb when it is on as it can be very harmful to you!

In summary we believe that in a freshwater aquarium it is unlikely you would need a UV steriliser however it may be worth getting one. It is more likely you would need one in a marine aquarium although you must be careful when you decide to use it and be sure to pick the correct model for your requirements.