Choosing a UV sterilizer can be a little confusing because you have to consider the wattage and what exactly you want to target. You then need to accommodate that UV sterilizer with the proper flow rate which may not be as easy as you originally had planned.  

Which Brand?

Before choosing the right wattage, look at the two different brands of UV sterilizers. Pentair Aquatics and Aqua UV are the leading manufacturers for saltwater UV sterilizers that are going to stand up to your saltwater aquarium. They are designed to be used with salt water and are marketed effectively for this application too. They give you the necessary flow rate information and rate of sterilization you need to specifically target the particular ailment you need to eradicate.

  • Pentair - Larger in physical size, heavy-duty, and more aggressive UV doses with specific flow requirements to achieve those doses.  
  • Aqua UV - Slightly smaller in physical size and they offer a hang-on option for tanks that don't have a sump.  They use a slightly less aggressive dose of UV based on the recommended flow rates but still give you sufficient information to achieve effective sterilization.

Rate of Sterilization

This is the measurement of how strong the UV rays are.  It is measured using µWs/cm² which is probably a foreign unit of measure to most of us but that doesn't really matter.  UV sterilizer manufacturers will provide you with a flow rate, that will achieve a certain level of sterilization with the said UV sterilizer. Different ailments require different rates of sterilization to effectively be eliminated.  

Bacteria and algae are easier to kill and will succumb to lower levels of sterilization. Parasites (protozoa) are more difficult to kill and will require higher levels of sterilization. When choosing a UV, you must choose what exactly you want to target or simply run two separate UV sterilizers that are set up differently.  


The more wattage, the more sterilization power you get. The more wattage, the larger the physical size of the UV.  With that in mind, always use the manufacturer's recommend tank size requirements. Don't get a UV sterilizer that has a maximum tank size rating smaller than your aquarium system.  You can go larger, but don't go smaller because it just won't work.

Flow Rate

With each UV sterilizer, you're going to get specific flow rate recommendations which is how fast water needs to flow through the UV to hit a particular level of sterilization. The slower you go, the higher rate of sterilization will be achieved because you get longer contact with the UV rays with each pass through the UV. Faster flow means a lower level of sterilization because you get less contact time. 

As we mentioned earlier, this is typically divided up into two camps when selecting a UV for a saltwater aquarium. Because bacteria and algae are easier to kill, you can run a faster flow rate and still achieve sufficient sterilization. If parasites are your target, then slower flow rates will be required. 

Choosing The Right UV Sterilizer

Installation matters here because the rate of flow you can provide may be limited by your desired installation. Most folks prefer to use the return pump because it is easy and hides the UV sterilizer down below the tank.  Alternatively, you can set up a closed-loop off the display tank using a dedicated pump which gives you the freedom to control flow but is a more cumbersome installation.  You could also choose to run dual return pumps with two UV sterilizers, each tuned at different flow rates to target different ailments. 

Learn More with BRStv: How to Install a UV Sterilizer, Set the Right Flow Rate, & Avoid Mistakes!

Let's produce an example of how to choose the right UV. The tables below are pulled directly from the product descriptions. In this example, we are finding a UV sterilizer to filter a 120-gallon saltwater aquarium. Reference the Maximum Aquarium Size outlined by the manufacturer. 

1. Select the appropriate wattage based on your tank size. Never go smaller but you can go larger in terms of wattage.

2. Verify you can supply the flow rate you need to achieve based on what you want to target. 

Notice the rates of sterilization measured in µWs/cm² below and the corresponding flow ranges. This is the rate of flow that you must achieve to target the particular ailment you want. You can only choose one and the flow rates are listed as a range. As long as your produce a rate of flow within that range, you can effectively achieve that level of sterilization. 

Since your 120-gallon tank likely has a return pump moving 360-600 GPH already, targeting Algae and Bacteria should be easy by installing the UV inline using your return pump. If you want to target protozoa, you will probably have to get a separate dedicated pump to install the UV sterilizer off your display tank and accommodate that slower flow range.

Pentair 25 Watt UV

Model  Maximum Aquarium Size No. Lamps/Watts Water Flow Rate Algae and Bacteria 30,000 µWs/cm² Suggested/Maximum Water Flow Rate
180,000 µWs/cm² Suggested/Maximum
Input Watts Dimensions (Inches) Inlet/Outlet
Smart UV 25 130 Gallons 1/18 472 GPH/788 GPH 79 GPH/131 GPH 18 29" x 3.5" 1.5" Union


What if you need to target parasites but still want to run the UV using your return pump? This can be accomplished by upsizing the wattage of the sterilizer. See the table below for the 50 watt UV. You can now hit the recommended flow range for parasites (protozoa) using your 330-600 GPH return pump. You won't need to slow down your return which reduces the effectiveness of your filtration and you can still hit the rate of sterilization for parasites.  While it is safe to say this UV is oversized for your 120-gallon tank, you're accommodating your particular installation and achieving the same level of sterilization. 

Pentair 50 Watt UV

Model  Maximum Aquarium Size No. Lamps/Watts Water Flow Rate Algae and Bacteria 30,000 µWs/cm² Suggested/Maximum Water Flow Rate
180,000 µWs/cm² Suggested/Maximum
Input Watts Dimensions (Inches) Inlet/Outlet
Smart HO UV 50 330 Gallons 1/50 1560 GPH/1980 GPH 260 GPH/330 GPH 50 30" x 6" 2" Union