UV Clarifier maintenance: Basic care and repairs

“Most people who keep a pond, take an interest in their equipment, know what’s in there and know how to take care of it, and rightly so,” says Swell warehouse manager Phil Cross.

“Unfortunately,” he adds, “some people like the idea of a decorative pond, like looking at it, but don’t like the idea of looking after it. They don’t realise that by not maintaining the equipment they are damaging the health of what’s in the pond.”

A UV clarifier is an ingenious concept. Your pump sends water into the clarifier and the water passes over the quartz sleeve that contains the UV tube. The UV rays “zap” the algae and send it into the filter box where it encounters your filter’s beneficial bacteria. The filter box acts as a sewage box and sends purified clear water back into your pond.

According to Phil many problems with UV clarifiers are brought on by a lack of simple maintenance and care. Phil oversees any returns – products that are sent back to Swell by customers who think their kit is not working. As with many products Phil finds that the faults could have been prevented with a bit of TLC.

As well as manning the testing bench at Swell, Phil also keeps a pond himself, so he knows first hand the problems pond keepers can face.

He said: “I have a koi pond, about 10ft x 7ft x 5ft deep. If I was going to get a filter now I’d probably go for one of the Oase filters that we sell, but I’ve had this pond since before I worked for Swell and I have on it a Lotus Green Genie 48,000. It is not considered at the high end of the market like Oase but to be honest, I have no complaints about it. It has a UV clarifier built in and I replace the tube once a season. Bear in mind I keep it switched on from February to November usually and like everyone else my pond has faced problems with blanketweed and so on.”

Phil added: “Not many people won’t encounter problems with blanketweed at some point, or greenwater which is suspended algae. You must treat these things not just rely on your UV clarifier. This is why we sell these treatments. Some people may not like the idea of having to change UV tubes, but it is a must,” says Phil.

“You wouldn’t consider not having your car serviced, not changing the oil and replacing worn tyres. UV clarifiers are the same. The light may be on but after a while they lose their effectiveness.”

So what if your UV clarifier is not working? The chances are, the problem is one of two things – either the UV tube has blown or the quartz sleeve has cracked. Tubes will of course blow, just like your light bulbs at home and the delicate quartz sleeves can also be vulnerable, no matter what brand you buy. The quartz can crack if you have been too rough during cleaning or if some grit has got into the thread.

Sometimes it can be difficult to determine whether your UV is working. Since looking at a UV bulb can damage the human eye, most units have a safety device which turns off the bulb if you attempt to remove it while the unit is plugged in, which could lead you to think that it’s not working. To overcome this problem, many units are fitted with a viewing window (which you need to keep free of dirt) to allow you to check whether the unit is on, without harming your eyesight. You may need to block out natural daylight in order to see this working.

How do I clean my UV clarifier? First follow the golden safety rule. Make sure you isolate it unplugging both your pump and clarifier or you will end up very wet or very electrocuted. Then follow this simple guide to how to strip down, clean and maintain your UV clarifier.

You must never look directly at a UV tube, it will hurt your eyes. The tube glows blue so if it’s working you will see a blue light behind the viewing window. The UV clarifier Phil is dismantling here is the Oase Bitron 55, an excellent choice of clarifier.

The unit is very simple to open and once you’ve opened it up you can remove the UV tube and quart sleeve. Remember to never touch either with your hands, always a clean lint-free cloth. It is essential that the quartz is crystal clear. Your greasy finger prints will not help the cause. Quartz is a special material because unlike glass it lets UV rays through. Oils in your fingerprints cause solarisation on the tube which means it blackens and prevents the UV getting out. You may have noticed on fluorescent tubes in your home, the ends become dark, this shows they are reaching the end of their life. This is true of UV tubes.

Remove the locking collar. It is quite common for these pieces to crack, particularly in a heavy frost. Bits of grit in the thread can also cause problems, so ensure everything is kept clean.

Twist off the quartz sleeve. Remember to grip it with a cloth or paper towel. Then you can get to the UV tube. Remove that as well.

Inspect the O-ring. This is what protects your electrics from the elements, so if it gets cracked, water will get into your electrics.

Give the quartz sleeve a clean. Even if it looks clean, it’s worth giving it a buffing. If you are satisfied there are no problems with cracked parts, grit or dirty tubes, you can replace your tube.

As you replace the quartz sleeve around the UV tube, make sure you have put the O-ring back on properly. Phil said: “People don’t realise you have to tighten things quite a lot in order to put pressure on the O-ring, this is what creates the seal.”

There is a second O-ring, above, which must line up with the groove inside your unit, below.

You may notice that the spinning component of your UV clarifier’s housing seems loose, this is natural, as long as it is in place a little movement is ok at this stage.

The Oase clarifier that Phil demonstrated above had been maintained pretty well, but not all equipment we receive back is so clean and tidy. This tube (below) from an Oase Biosmart, that we received back from a customer, was never going to produce effective UV with such a filthy quartz sleeve.

A sleeve as mucky as this one would need a good soaking in warm water. Remember the sleeve is very delicate so don’t use boiling water. If it has limescale on it which is common in hard water areas use some white vinegar.

There is a plethora of problems with this tube. The quartz sleeve is filthy, the locking piece is cracked, and water has been allowed to enter the electrics – and amazingly this piece of kit is only 18 months old.

Phil concludes: “If the water quality in your pond is very poor then the UV clarifier is going to really be fighting to work.”


  • Avatar Julie Posted 10/06/2014 at 5:48 pm | Permalink | Reply

    Hi I bought a uv from reputable dealer and I replaced my original blown one that has been in since I bought the unit 3 years ago. I noticed that all of a sudden after 2days my water was not improving any more. I checked and the bulb had blown. Now it’s a 55w from a bitron filter. They have said they will kindly swap it , but I was thinking could there be a fault with the uv to cause this. Or is it simply just a poor quality or faulty bulb. Everything is clean grit free etc no rusty parts. I don’t want to find it happen again when I replace it. Would you recommend I buy the same bulb Phillips it came with?

    Bulb was shot uk ltd and was correct bulb 55w 4pins



    • Avatar Cat Byrne Posted 19/06/2014 at 11:39 am | Permalink

      Hi Julie,

      It is unlikely to be an issue with the unit itself, probably just a faulty bulb. The same bulb should be fine and if the bulb works the unit should continue working for years!

      Hope this has helped

  • Avatar Barry Posted 20/09/2014 at 8:15 pm | Permalink | Reply

    Hi ,i have a similar problem to the one above, i have the 9watt clarifier ,it is only a year old but keeps blowing the bulbs, i was wondering if you could check it over for me ,
    many thanks Barry

  • Avatar Barry Posted 20/09/2014 at 8:17 pm | Permalink | Reply

    ps it has blown 3 bulbs straight off ,cheers

  • Avatar Malcolm Posted 26/03/2015 at 12:25 pm | Permalink | Reply

    I hope you can help, I have just serviced Bitron UV unit for the new season. With new 18 w tube
    When switching on lamp lights for just 2 secs then does not work.

  • Avatar terry Posted 25/05/2015 at 11:37 am | Permalink | Reply

    Hi wonder if you could help replacing 55 watt uv bulb in 30000 filtercleer
    replaced but uv blue light doesnt come on many regards Terry

  • Avatar mitch eastwick Posted 04/04/2017 at 4:21 pm | Permalink | Reply

    could you tell me how to put the55w bulb and bitron clarifier back together it seems to not close fully? thanks

  • Avatar mitch eastwick Posted 04/04/2017 at 4:23 pm | Permalink | Reply

    could you tell me why my tube wont go into the clarifier properly

  • Avatar Chris fLACK Posted 28/08/2017 at 2:22 pm | Permalink | Reply

    Please help. I changed the bulb in my Bitron 55C 55W unit and the light that indicates the bulb is working is not lit. i feared the fault to be a faulty lamp so bought a replacement, still no indication. I have checked the electrics through to the bulb but the bulb refuses to light. This leads me to a possible fault with the housing unit? The filter is only 12 months old, so who can i go about getting a replacement unit under warranty, or indeed does the warranty from OASE cover this ?

    Please help as my ponds water is starting to become cloudy and green and i need to solve this issue swiftly.

    Thank you

  • Avatar Paul Collis Posted 25/04/2018 at 9:22 am | Permalink | Reply

    The fuse has blown and after replacement the light does not work.
    I have checked and the lamp looks OK not brown at ends etc.
    Is it worth getting another lamp or is it likely to be something else.

  • Avatar Jackie Posted 03/05/2018 at 1:49 pm | Permalink | Reply

    I opened my tetra pond clarifier because it made a rattling sound and glass came out so i assumed it was the uv bulb ,but the outer quartz sleeve did not come out and the bulb is not broken looks like its the sleeve how do i replace it?

  • Avatar michael Posted 23/05/2018 at 8:17 am | Permalink | Reply

    hi could you please tell ,we had power cut after 4 hours when electric came on my pump jamm for some reason and the uv same item in your picture has been running without water i guess 3/5 hours , do i need to replace the bulb as i only replaced april this year thank you michael

  • Avatar David Simons Posted 20/08/2018 at 2:13 pm | Permalink | Reply

    I have a Hozelock Vorton 36 and the other day my wife came in in a panic and told me that the pond was leaking. On inspection my UVC was leaking water where the main housing had split. On closer inspection and after turning off the power I found that the main housing rigid plastic had become paper thin and could be punctured just by pushing you finger through it. The unit is only 1 or possibly 2 years old so my question is, is this a common problem that the UV is affecting the polymers of the plastic and if so are plastic units fit for purpose?

    Thanks in advance


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