Proper installation of your UV sterilizer is important because when done wrong, you can drastically reduce the effectiveness of your UV.  Proper wattage, how many times water passes through per hour, and how it is plumbed all play a role to ensure optimal sterilization.  Simply put, when plumbed incorrectly a UV will work but you're just not reaching the full potential and a larger portion of the pests and algae can still survive.

Learn More with BRStv: How to Choose the Right UV Sterilizer For Your Saltwater Tank

Plumbing a UV Sterilizer

A UV sterilizer needs to be plumbed using a "closed-loop" on your display tank. You should avoid pulling from the sump and returning back into the sump because you will essentially bypass other forms of filtration and recycle the same water over and over again through your UV. 

Option A - Sump Configuration

Water should be pulled from the sump, go through the UV, and then returned to the display. You want all of the water to pass through the UV as it makes its way through your filtration before heading back into your display. This can be plumbed inline using your return pump and is often the preferred route for this very reason, you don't need an extra pump to run the UV.  It also allows you to mount the UV down below your tank, out of plain view. 

Option B - Display Only

Alternatively, you can set up a closed-loop on your display alone which means the water will pull from the display, pass through the UV, and then return back into the display. This is arguably the most effective approach because it is easier to tune the flow rate correctly and works independently of your return pump and filtration.  That said, it requires a dedicated pump to feed the UV and is not as easy to disguise the whole setup. 

Setting the Flow Rate

Flow rate is everything with a UV because it controls the contact time.  The slower the water moves, the more contact time it has with the UV rays meaning the more effective those rays can be at killing things. That said, this also affects how many times per hour you can recycle the entire water volume through your UV per hour which is also important.  The balance of these things will ultimately control the rate of sterilization. 

A UV sterilizer should be tuned based on the particular goal because the level of sterilization required to kill bacteria and algae is different than what is required to kill common aquatic parasites.

Tuning Flow For Bacteria & Algae

This would be designed to reduce cloudy water from bacteria blooms, inhibit cyanobacteria, and stop the spread of nuisance algae.  The most common rate of flow for reducing bacteria and algae using a UV is 3x - 4.5x total tank volume per hour. For a 50 gallon tank, you should be moving 150 - 225 GPH through the UV sterilizer. 

This just so happens to be the very common rate of turnover we run through our sump and return pump which works out for the common application of installation the UV inline using your return.  You can choose the UV sterilizer based on these flow rate requirements for your particular tank. 

Tuning Flow For Fish Parasites

To target and kill Ich, Flukes and other common fish parasites is much more difficult and requires slower flow through the UV sterilizer which increases that contact time.  As much as 50-75% less flow compared to killing off bacteria and algae.  A turnover rate of 0.5x - 1.5x total tank volume per hour is generally the target. A 50-gallon tank would require 25 - 75 GPH through the UV sterilizer per hour to kill parasite.

In this case, you could increase the wattage of the UV sterilizer to accommodate the flow rate you have running through your sump/return pump or simply run a separate dedicated pump tuned to the slower flow rate.  

Running Dual Return Pumps

Running two return pumps has some great benefits. First, it gives you a backup pump should one fail, you always have that secondary pump to keep water moving through your tank. Second, you can run two UV sterilizers, tuned at different flow rates to target bacteria, algae, and parasites, and achieve the most complete UV sterilization. While it might seem like a bit much, if protecting your tank is the goal, this is the way to go. 

Plumbing Considerations

  • Most UV sterilizers are designed to be mounted vertically to avoid air getting trapped inside. Trapping air can cause things to heat up and damage the UV.
  • Plumb your UV in a way so that it is easy to remove and replace the bulb which is required to be done annually.
  • Use a flow meter to monitor the flow rate and confirm you got it right.  The Neptune Systems FMK is a great solution for Apex users.
  • If you don't have access to a flow meter, you can measure the flow by doing a manual bucket test.  Simply time how long it takes to fill a 5-gallon bucket of water after passing through your UV. You can use that time to calculate the gallons per hour.  For example, if the flow can fill a 5-gallon bucket in exactly 1 minute, it will be moving 300 Gallons of water per hour.