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How to install a pond UV clarifier

Updated: 22 October 2026

The box is in the shed and the pump is already running. For an Evolution Aqua evoUV the order is fixed: put the housing on the pipe, prove the quartz sleeve is dry inside, then stop. A qualified electrician connects the supply. This page is that sequence for the four units on our [UVC pond clarifier comparison](/hub/garden-ponds/uvc-pond-clarifier). Wattage stays on the [buying guide](/hub/garden-ponds/uvc-pond-clarifier/sub/uvc-pond-clarifier-buying-guide). How long green water takes stays on the [green water page](/hub/garden-ponds/uvc-pond-clarifier/sub/uvc-pond-clarifier-green-water). Peter F. is not wiring your garden. A qualifying purchase can earn us a commission at no extra cost to you.

The box is in the shed and the pump is already running. For an Evolution Aqua evoUV the order is fixed: put the housing on the pipe, prove the quartz sleeve is dry inside, then stop.

Our top picks

Evolution Aqua Evolution Aqua evoUV evo25

Best overall

Evolution Aqua Evolution Aqua evoUV evo25
8.8/10about £129.99
View offer
Evolution Aqua Evolution Aqua evoUV evo55

Best value

Evolution Aqua Evolution Aqua evoUV evo55
8.8/10about £199.99
View offer
Evolution Aqua Evolution Aqua evoUV evo110

Rank 3

Evolution Aqua Evolution Aqua evoUV evo110
8.6/10about £284.95
View offer
On this page
  1. 1.Where the unit sits on the pipe
  2. 2.Seals before electricity
  3. 3.Mounting and weather
  4. 4.The supply is the electrician’s job

Where the unit sits on the pipe

On a pump-fed system the evoUV is the first item after the pump and before the filter. On a gravity-fed system it goes after the filter, on the return to the pond. Do not merge that with a manual that always wants the lamp after the filter. Ball valves either side are recommended on gravity systems so you can isolate the housing. Either end can be the inlet. You still need room to pull the quartz sleeve, which on the evo30 and evo55 means a body the maker lists at 990 mm. The evo25 is 540 mm. Leave that pull-out clear of the fence. Reviewers already call the evo25 fiddly because the cable twists with the end caps.

Seals before electricity

The lamp stays out until the sleeve has held water. Fit the quartz, the O-rings and the locking nuts, run the pump, and look for a dry socket. The manual excludes water damage from a badly fitted quartz sleeve. Only then do the lamp and the end cap go on. On the evo25, evo30 and evo55 the stepped hosetails cover about ¾ inch up to 1½ inch. Cut off unused steps. The clip is not in the box. One UK review of the evo30 says the hosetail thread jumps under side load, and the O-ring pops off if you go past hand tight. The evo110 is 2 inch, and the manual says no UK flexible fittings are supplied. European 63 mm adaptors are not the UK kit.
Evolution Aqua Evolution Aqua evoUV evo25

Testsieger

Evolution Aqua Evolution Aqua evoUV evo25
8.8/10about £129.99
View offer

Mounting and weather

IP65 in the manual means jet-resistant, not submersible, and these amazon.co.uk pages do not print that rating. If the housing will be splashed, mount it the right way up. A tilt that leaves an end cap as the low point pools rain on the seal. One UK review of the evo55 says the ballast seal let rain in within a year and tripped the house electrics. That is one report, not a rate. You will not see a useful glow in daylight. Reviewers check after dark. A glow is not a clean quartz or a young bulb. The Health and Safety Executive describes UV injury to the cornea and the skin. Do not look at the lamp, do not run the unit open, and disconnect before a lamp change. The koi page is about size, not a different electrical ritual.

The supply is the electrician’s job

The manual says a qualified electrician should install the unit, on an RCD whose trip does not exceed 30 mA, without an extension lead, and with the permanent connection that section describes. You can plumb, wet-test and mount. Conductor colours in the manual are for the electrician, so they are not repeated here. Approved Document P in England puts garden pond pumps inside Part P. In the 2013 edition, notifiable work is a new circuit, a new consumer unit, or work in a bath, shower, pool or sauna room. A garden pond is not named there as a special location. The electrician checks the current GOV.UK edition. Wales, Scotland and Northern Ireland run their own regimes. Call them too if the cable is damaged, if the RCD will not reset, or if you are adding a new circuit. A tripped RCD is a reason to stop.

Common questions

Does the UV go before or after the filter?
On a pump-fed Evolution Aqua setup the evoUV is first after the pump and before the filter. On a gravity-fed setup it sits after the filter on the return. A manual that always wants the lamp after the filter is not a correction. Look at whether a pump pushes into the filter, or water falls through and is pumped back.
Can either end be the inlet?
Yes. The manual does not give a mandatory flow direction, so you can turn the body to suit the pipe. You still mount it the right way up if it will be splashed, and you still leave room to withdraw the quartz sleeve. Either end is about the hose, not about standing the unit on the electrical cover.
When do I fit the lamp?
After the wet test, and only if the socket end has stayed dry with the pump running. Quartz, O-rings and locking nuts are proved first. Water in the socket is outside the warranty. If you see a weep, fix the seal and test again before the lamp goes in.
How tight is hand tight?
Tight enough that your hand will not comfortably go further, and no further. On the evo30, going past that point popped the O-ring off, and side load made the hosetail thread jump. Cut unused steps off the ¾ to 1½ inch tails. The clip is not supplied. The evo110 does not use these tails.
Can I submerge an IP65 unit?
No. IP65 in the manual is jet-resistant, not a licence to drop the unit in the pond. These amazon listings do not print the rating. Mount it the right way up and keep rain off the ballast end. The evo55 rain report is one account, and still a reason to shelter that end.
Do I need an electrician?
The manual says yes: a qualified electrician, an RCD not exceeding 30 mA, no extension lead, and the permanent connection that section describes. Plumbing and the wet test are yours. A new circuit, a damaged cable, or an RCD that will not reset is not. A 2013 reading of Approved Document P is not the current rule in every UK nation.
What is different about the evo110?
It is a 2 inch body, and the UK flexible fittings are not in the box. European 63 mm adaptors are a different kit. You still wet-test before the lamp, and the electrical end is still the electrician’s job. The extra wattage does not change that.

Related pages

Pond pump comparison

UVC pond clarifier

Best UVC pond clarifier for the pond in front of you

What size UV clarifier for my pond, by sun and flow

UV clarifier for green pond water, not blanketweed

Koi pond UV clarifier size for sun and heavy stock

Sources

Public UK and maker sources for this comparison. Listings and prices were taken from amazon.co.uk on 19 October 2026. IP65, wattages for the evo25, evo30 and evo55, and the flow figures are from the manufacturer manual, not from those three amazon pages.

  1. Evolution Aqua evoUV (retrieved 19 October 2026)
  2. Evolution Aqua evoUV installation manual (retrieved 19 October 2026)
  3. Evolution Aqua support: recommended flow for an evoUV 55 (retrieved 19 October 2026)
  4. FishLife: how to choose UV pond clarifiers (retrieved 19 October 2026)
  5. HSE: optical radiation (retrieved 19 October 2026)
  6. Water Garden Ltd: how often to change a UV bulb (retrieved 19 October 2026)
  7. Electrical Equipment (Safety) Regulations 2016 (retrieved 19 October 2026)
  8. Approved Document P (retrieved 19 October 2026)