March 29, 2020

Your water isn’t looking as clear and pristine as you remember from last year. Everything is up and running. You have your UV light on, and you think it’s doing its job but your water remains green and cloudy. It could be time to change your pond UV light bulb.

Nothing is more exciting than installing your pond UV light (link to how to do that). Knowing that in a matter of days the improved water quality will let you see your fish again. As the seasons go on, your light loses its oomph! Yes, to us the light still looks the same, but the power it exudes diminishes over time.

How To know when to change my UV light bulb

Even though your bulb lights up, it does not have the power it once had. This occurs after about 10,000 hours of run time. 

Typically where I live the UV light is on from April to September. Six months running 24 hours. That’s 180 days X 24 hours = 4,320 hours in a season. Most Uv bulbs begin to lose their strength and effectiveness around 10,000 hours. 

About every 2 and a half seasons your UV light bulb will need to be replaced. If you go by this schedule and change your bulb before you start to see symptoms of diminished strength, you will keep your pond clear without a hitch!

Which UV Bulb Do I Use

When it comes to UV light bulbs, it’s not a one size fits all solution. There are many choices when it comes to UV lights so be sure the bulb you get will fit in your light.

The manufacturer of your UV light will have a list of recommended bulbs, either on their website or right on the light itself. There are also aftermarket bulbs that will fit your style of UV light. Be sure your light model is on the bulb compatibility listings.

Below are basic steps for changing your UV light bulb. The light pictured and used in this tutorial is an Emperor Aquatics UV sterilizer with a 40 watt bulb.

Not all UV lights are built the same exactly the same, but they all share the same principal. Water flows from one end of the light to the other. 

The bulb is encased in a clear tube, usually crystal. The longer the water is exposed to the UV light the more effective it is. Our article on choosing the right UV light (link to article) explains more on flow rates, and getting the most out of your UV pond light setup. 

Steps To Change Your Pond UV Light Bulb

GFCI outlet

This goes without saying, but the first step is to be sure your light is not plugged in.

UV light bulb change

Most UV lights have clear tube that houses the bulb. Using a pair of channel locks or a pipe wrench loosen the nut that holds the bulb in place.

Removing UV light bulb

Slide the bulb from the sleeve. Do this with care. If it is not pulled straight out you run the risk of breaking the bulb.

crystal tube in UV light

This is a good time to remove your crystal tube, and clean it. Some UV light designs have a wiper system that allows you to "wipe" the clear tube without taking it apart.

UV light bulb change wire harness

Disconnect the wire and take note the way the bulb is plugged in. This will ensure you have the correct replacement bulb. The bulb in this tutorial uses a 4 prong wire harness.

taking pond UV light apart

Unplug the old light and plug in the new one. Then slide it back into place.

pond UV light bulb change

Be sure all of your connections are water tight. Your light is now ready to be put back into service, at full power!


Set yourself up for success this season, and if you don’t have a UV light yet get one here (link to Amazon for our recommendation). Not sure which one will suit you best, check out our article on choosing the right UV light (link to article). If you are already using a UV light, be sure it is operating at its full potential and change your pond UV light so you can enjoy this season without a hiccup.

Wishing you clear water and a relaxing season. Until next time, enjoy your backyard water garden


About the author


I love being outdoors and hands on DIY. If you share my passion, you are in the right place. If I can help one person surprise themselves with the success of a project, then this website is a success.

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