Reef keepers have long debated whether the constant use of a UV sterlizer is helpful or harmful to a saltwater reef tank. In essence, a UV sterilizer has a UV bulb in a water tight compartment that will kill or zap undesirables in the water that pass through the unit. Undesirables include free floating algae spores, parasites and troublesome bacteria such as heterotrophic bacteria, which are considered “scavenger” bacteria and can bloom, causing cloudy water.

To UV or Not to UV?

A UV will not kill beneficial bacteria that are in the sand bed and live rock since they are not free floating. However, the key question is whether the sterilizer will also kill free floating microorganisms that are beneficial to corals? Are the benefits worth this risk?


Before I delve into that question, let’s take a closer look at the reasons why one would use a sterilizer on a constant basis. What about preventing fish disease? A UV can reduce the amount of parasites in the water column, making it easier to treat an outbreak and reduce the impact. However, it won’t prevent or eliminate disease. Remember, a UV will kill free floating microorganisms and ich is not free floating in all stages of its life.


Using UV For Water Clarity?

Ok, how about using one to maintain crystal clear water? A UV will certainly help in this regard since it does kill free floating algae spores and problematic bacteria. I used two AA Aquarium Green Killing Machine 24W UV Sterilizers to successfully to clear up cloudy water caused by a bacterial bloom in my 187 gallon tank. They were relatively inexpensive and very easy to install and then remove when I was finished using them. The difference over a couple of days was amazing.


Cloudy aquarium water

Before use of UV Sterilizer



2 Days After Use of UV Sterilizer


Just keep in mind that a UV will not wipe out something like hair algae attached to rocks or corals. Again, it has to be free floating.


Do I advocate using a sterilizer 24/7 on a reef tank to take advantage of the benefits? No. I endorse using other means to achieve the dividends offered by a UV sterilizer. To prevent fish disease the best course of action is to quarantine all new arrivals in a separate tank. As for water clarity, I am a proponent of using activated carbon to keep things crystal clear.


I do believe UV sterilizers are useful in small doses to rectify a problem such as a bacterial bloom. I have no proof mind you, but I am leery about the detrimental impact they might have on culling back the population of free floating microorganisms that are beneficial to corals.


If you are looking for additional insights and information, please explore my many other reef tank and SPS related articles as well as my YouTube channel. For an even deeper dive into reef tank care you can check out my Reef Keeping Master Class. This online course is an immersive and one of a kind educational tool designed to help reef aquarium hobbyists build and maintain a beautiful SPS reef tank. The course is a series of video presentations with some supplemental video from my YouTube channel. There are also quizzes to help students retain and understand the information presented in the course.


Reef Keeping Master Class – Learn More



Happy reef keeping!