How to select the right quartz sleeve and bulb for your UV

Ultra Violet Clarifiers are designed to work with filtration to clear green pond water. They do this by emitting ultraviolet light, which damages the tiny green algae cells that flow past it. Get the right sized UVC for your pond and they work brilliantly well, clearing green water and keeping it at bay throughout the season. 

But UV bulbs have a relatively short life and should be changed at least once a year, or even six-monthly sometimes to get the best out of the bulb from March through to September, when algae is most prevalent. 

Look up the wattage

There are many types of UV bulbs from 4 watts to 55 watts, two-pin, four-pin, and double-ended. Although many bulbs look similar, getting the wattage right is just as crucial as the length and pin type. 15 watt and 25-watt double-ended bulbs look identical, but a 15-watt unit won’t power a 25-watt bulb, and vice versa.

If you kept the box, your Ultra Violet Clarifier should state its wattage on the box, like 11 watts for example. If you don’t have the box, the instructions will state the type and wattage of the bulb that you need.

If you don’t have the instructions, look up the make and model of UVC you have here, and it should state it in the product information section. There may be a sticker on the actual unit too, and if there is, the wattage should be stated there.

Find wattages in the Product Information section

Remove the old bulb

If you can’t find or don’t know the make and model of your UV clarifier, unplug it and disconnect it from the mains. Turn the pond pump off, open up one end of the uv and carefully remove the old bulb. The bulb sits inside another glass tube called a Quartz sleeve, and that can be single or double-ended too, depending on the bulb type.

NEVER remove a bulb while the unit is switched on as the light that it emits is damaging to your eyes

Quartz sleeves are very fragile too, so be careful when removing an old quartz sleeve for cleaning, or replacement. Once removed the bulb should have a wattage printed on the bulb itself and maybe its type, like PL for example. And if you still get no joy, take a picture of it and send it to our customer services team who will be more than happy to help you.

Changing the bulb and quartz sleeve

Once the bulb has been removed, the quartz sleeve should also be removed and cleaned. The cleanliness of the quartz sleeve directly affects bulb performance as the UV light shines through the quartz and onto the water that’s being pumped past it. If the quartz sleeve is dirty or opaque light can’t penetrate through it so well and won’t be as effective. Clean the tube with a sponge and if it’s covered in limescale deposits soak the bulb in a bath of pump cleaner.

Inspect the rubber seals that hold the quartz in place. If they are perished replace them, as they need to be watertight and intact.

Wear gloves or hold the bulb and quartz with tissue paper while fitting, so no fingerprints or oil are left on them.

Be careful when removing the bulb or fitting a new quartz sleeve

Frequently asked questions on UV bulbs and quartz sleeves

What do I do if the quartz sleeve is cracked?

If the quartz is cracked it must be removed carefully, discarded and replaced. A cracked quartz will allow water to seep into the light fitting and damage it. 

What do I do if break the quartz while fitting it?

Quartz sleeves are incredibly brittle and sadly, very prone to breaking. If you break the quartz while fitting it, discard it and order another one. Quartz are not covered by any kind of manufacturer’s warranty against breakage.

I’ve changed the bulb but the water is still green?

A very green pond make take days or weeks to clear. First check that the bulb is actually on, and the best way to do this is to see if the hose tails glow in the dark at nighttime. If it is on, the unit may be undersized for the pond (recalculate pond volume,) or the flow rate may be too fast for the UVC to be effective on green algae.

Check the maximum flow rate for that model of UV. If necessary, slow the pump down with a valve, use a smaller pump or a bigger UV. Or fit a bypass so that only some of the water passes the bulb. That may be enough to make a difference.

How do I know if the bulb needs changing? 

A UV light may still glow long after its effectiveness. If the water is green the bulb should be changed or if you inherit a pond and you don’t know how old the bulb is, it’s best to change it for a new one. 

Can I put a more powerful bulb in my UV?

No, the ballast will only power the bulb it’s intended to. If you need more UV power you could add a second UVC inline, after the first one.

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Jeremy Gay is an author, lifelong fishkeeper, and aquatic specialist. He's a former editor of Practical Fishkeeping Magazine, UK editor at Reefbuilders, a former aquatic store manager, and has collected fish in Sri Lanka and the Amazon. He's been on tv and radio, contributed to Koi Carp and Gardeners World magazines, been a product tester, a judge, and a product developer. Jeremy is here to guide and advise you on all things tropical, pond and marine, from set-up to stocking, health, feeding to breeding, as well as solving many common fishkeeping problems along the way.


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