Ponds equipment

5 Best Pond UV Clarifiers – see the bottom of your pond

Last updated on September 30th, 2022

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There is a lot of miss information online about pond UV clarifiers, and I think that the manufacturers don’t help things, as they often seem to, let’s say, misguide, whether on purpose or not, about what they can actually do and kill. They also sometimes use the two types of unit names interchangeably, that is UV clarifiers and UV sterilisers, but they are, in fact, not the same. The problem is they use the word ‘Clarifier’ and ‘Steriliser’ interchangeably or both in the product titles like this “Pond UV Light Steriliser Clarifier Filter” It can’t be both, so which one is it?

I recently talked about the importance of choosing the right pond liner, choosing a pond aerator to help oxygenate the water, pond skimmers to help keep the surface of the water clean as well as choosing the right pond vacuum because these are great for cleaning string algae that a UV Clarifiers are unable to remove.

Pond vacuums are great for deep cleaning the pond floor. If you need to empty your pond for deep cleaning, a dirty water pump is also handy to have. It is also worth noting that some pond filters come with UV clarifiers already installed.

Best Pick

AllPondSolutions Stainless Steel Aquarium & Pond 55w UV Light Clarifier
This pond UV clarifier is suited to a large pond up to 60,000L in volume but they so sell larger and smaller models too. It has a stainless steel construction which increases the effectiveness of the UV light. The transparent panel in the out tube lets you see at a glance if the light is working. And you don’t have to worry about the clarifier overheating as it automatically shuts down if that happens. This thermal protection feature then waits until the clarifier reaches normal temperature and automatically starts it up again. These built-in safety conveniences allow you to use the AllPondSolutions Pond 55w UV Light Clarifier in any large pond. Overall, I think this is one of the best clarifiers as it's also easy to remove and clean the UV bulbs.


Evolution Aqua evo25 UVC Pond Clarifier
The Evolution Aqua evo25 UVC comes in a range of sizes for small to medium garden ponds. The evo25 takes a 25W UV light and can handle a pond up to 25,000L, smaller if the pond receives a good deal of sunlight. The two hosetail fittings are a standard size. The only variety of connections is that they fit both hard pipes and flexible hoses. So make sure that your pond system set-up is compatible before you buy. As most ponds owners will know, it's always possible. This pond UV clarifier is a good choice if you have a small to medium pond and a compatibly sized pond system as its also available in wattages from 15w to 75w

I’ll tell you who makes some of the best pond clarifiers, despite the fact they’re also guilty of using Steriliser/ Clarifier in their product titles. All Pond Solutions actually make some of the best models, such as this Allpondsolutions Stainless Steel Pond SSUV-55 Clarifier, and they have a few different size models with varying wattage ratings too. The problem is, that most manufacturers seem to do it. I think it’s just part of their marketing.

Fish pond which has green water caused by free-flowing algae that needs a UV clarifier
The fish pond, which has green water caused by free-flowing algae needs a UV clarifier

Firstly you need to understand that water clarity issues (green water) are caused by the abundance of nutrients in the water and exposure to sunlight. This becomes a breeding ground for tiny green single-cell organisms (free-flowing algae) that feed on phosphate and nitrate in your pond. They are very small, and in small numbers, you cannot see them. However, they multiply very quickly and in large numbers, this is when the water becomes green, and this is millions of free-flowing algae.

I discuss in more detail about choosing the right wattage bulb, how they work and why you need one in my buyer’s guide.

Knowing the difference between a UV Clarifier and UV Steriliser

Both types of units (clarifiers and sterilisers) are used to clean green water or prevent the water from turning green. The main difference between the two is the type of UV light used and the cost to buy them. UV clarifiers are what I would say 90% of people use. They use a UV light called UV-A which you can see in the chart above. It is a weak UV light on the spectrum of UV light. It’s not dangerous and is a safe UV light, even for humans.

Genuine UV Sterilisers use a UV light called UV-C (also on the chart) which is much more powerful, now this can kill bacteria and even parasites. However, they are extremely expensive, as much as 3 times more in price than a UV clarifier.

The problem I have is that I don’t think much of the bacteria in a pond will pass through a UV steriliser’s UV light. This is because they tend to live on things in the pond, such as the side of your pond, and so won’t pass through the UV steriliser. Parasites obviously live on a host, such as your fish, so they also won’t pass through the steriliser.

When I take all this into consideration, this is why I don’t think it’s worth me or most pond owners, for that matter, spending the extra money on a genuine UV steriliser and spending over £300. Luckily, the more affordable UV clarifiers, such as this AllPondSolutions 55w Aquarium & Pond UV Light Clarifier, work brilliantly at making your green water clear, and they do the same job when it comes to making your water clear.

Blagdon 5W Mini-Pond UV Clarifier ,Black

How a UV clarifier works is that the water passes through the clarifier and circulates around the bulb that emits the blue UV-A light. This causes a process known as flocculation where the single cell free-flowing green algae start to clump together until they’re big enough to be collected by your standard filter system. A UV steriliser works in exactly the same way too.

pond UV purifier to keep the water clear and algae free

When it comes to size, you can get them as small as 9w for very small ponds. However, I would recommend something between 18w and 55w for most people. 55w is usually a good middle ground for most ponds. This Evolution Aqua evo25 UVC is also a great choice and it’s also available in 15w, 25w, 30w, 55w, and 75w so there are plenty of models available to specifically suit the size of your pond.

When choosing a UV clarifier the wattage you need also depends on the size of your pond, how well it’s stocked as well as its exposure to the sun. To give you an idea, Evolution has an excellent table to help you choose the right model.

Evolution Aqua evo25 UVC

Pond pumps with built-in filters and UV clarifiers

My guide on the best pond clarifiers only includes standalone UV clarifiers. This means they need to be connected to your pond pump and installed before the pond pump. You can also get a new pump, especially for the clarifier. However, you can get some all-in-one pond pumps with filters that have a UV clarifier built into them but they are usually only 9w.

Remove them in winter

I would also recommend draining and removing your UV clarifier in winter and storing it away, and then installing it again in spring.

Give it time to clarify the water

Finally, seeing results with a UV clarifier or UV steriliser can take some time. If you have a larger one in relation to your pond size, you might see results in a couple of days. However, in around 14 days, you should start to see crystal clear water again to a point where you can see the bottom of a pond, even if it’s a deep pond.

Best Pond UV Clarifiers Review

1. AllPondSolutions Stainless Steel Aquarium & Pond 55w UV Light Clarifier

Best Pick

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allpondsolutions Stainless Steel Aquarium & Pond 55w UV Light Steriliser | SSUV-55 Pond & Fish Tank Clarifier - Helps Remove Algae and Greenwater

The AllPondSolutions Stainless Steel Aquarium & Pond 55w UV Light Clarifier works for large ponds up to 60,000L. If your pond isn’t this large, there are other sizes available, including those with an 18W UV light, a 36W UV light, and a 110W UV light.

This UV clarifier’s stainless steel construction, according to the manufacturer, is 30% more effective than comparable plastic found in other models. This increases the effectiveness of the UV light clarification by 50% or more, so your green algae won’t stand a chance.

There’s a transparent panel in the outer tube so you can easily see if the light is on and working. The quick release for taking the bulb out lets you clean it regularly or change it every year.

The thermal protection system automatically shuts down the unit if it’s in danger of overheating. You don’t have to worry about when to restart it as it also does that automatically when the unit has cooled down enough.


  • Pond UV clarifier designed for large ponds up to 60,000L.
  • Stainless steel shell increases UVC clarification.
  • Fits 30mm; 44mm; and 51mm hosetails.
  • Built-in thermal protection feature.
  • Transparent panel to see that the unit is on.
  • The minimum flow through rate is 8000L/h.
  • The maximum compatible pump is 14,000L/h.
  • The power cable is 5m.
  • Quick release for replacing the bulb.
  • Two-year warranty.

Our recommendation

The AllPondSolutions Stainless Steel Aquarium & Pond 55w UV Light Clarifier is one of a range of clarifiers for all sizes of ponds. Pick the one that’s the right size for your pond and rest assured that it won’t overheat – the advanced thermal protection system prevents that.

The AllPondSolutions Stainless Steel Aquarium & Pond UV Light Clarifier is the Best Pick in my review.

2. Evolution Aqua evo25 UVC


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Evolution Aqua evo25 UVC

The Evolution Aqua evo25 UVC is a pond clarifier for smaller ponds. If your pond is in full shade and is 25,000L or smaller, this 25W UV light is the right size for you. However, if the pond is in partial shade or full sun and is this size, you need a more powerful UV light.

The full range of Evolution Aqua pond clarifiers includes a 15W bulb model, a 55W bulb one, and a 75W bulb unit to suit the size and location of your pond.


  • UVC light clarifier for smaller ponds.
  • Rating of IPX5 for waterproofness.
  • Maximum pond size of 25,000L if in full shade.
  • The maximum pump flow rate of 10,000L/hr.
  • Takes a 25W bulb.
  • Has two 3.75cm hose tail fittings (included).
  • Use with flexible hose or hard pipe.

Our recommendation

The Evolution Aqua evo25 UVC is a good size for small ponds in the shade or even smaller ones if they receive quite a bit of sunlight during the day. Be sure to check if your water pump output is compatible with this clarifier’s needs though.

The Evolution Aqua evo25 UVC is my Runner-up for its range of sizes for small to medium-sized ponds.

3. Yamitsu Algae Master Pond UV 55W

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Yamitsu Algae Master Pond UV 55W

The Yamitsu Algae Master Pond UV 55W has the same wattage of the bulb (55W) as our Best Pick, the AllPondSolutions model, but this manufacturer states that the Yamitu model is best for ponds of 27,000L or smaller.

This model is made from UV stabilised materials. So we suspect that’s plastic, although it’s not stated in the sales blurb or on the manufacturer’s website.

But the manufacturer’s website does go into quite some detail about how to place this clarifier into your existing pond filtration system (use glue, not included). This UV clarifier can connect to a wide range of flexible pipe sizes so should fit into most pond systems.

This model is also available in a 30W UV light for ponds up to 20,000L.


  • Pond clarifier made from UV stabilised materials.
  • Can connect to 1.25cm, 2.0cm, 2.5cm, 3.2cm and 3.8cm flexible pipe.
  • Fit into your filtration system in line after the pump.
  • Comes with a 55W UVC lamp.
  • Bulb easily removed for cleaning.
  • The max pond size with a 55W bulb is 27,000L (in partial or full shade; from the manufacturer’s website).
  • The max flow rate is 15,000/hr.

Our recommendation

The Yamitsu Algae Master Pond UV 55W is worth a look if your pond system has an awkward size of pipe – you may find a connector here that fits.

4. Blagdon 5W Mini-Pond UV Clarifier

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Blagdon 5W Mini-Pond UV Clarifier ,Black

The Blagdon 5W Mini-Pond UV Clarifier is for those with small ornamental ponds. These ponds still get their share of algae but don’t need the larger UV clarifiers. The 5W light in this model handles small ponds up to 4,000L. Check also the recommended maximum pump flow rate as it’s quite low.

If you have a slightly larger pond or your pond water is hit by a lot of sunlight, consider the model that has a 9W UV light.


  • Mini-pond UV clarifier for small ornamental ponds.
  • UV light has 5W of power.
  • For ponds up to 4,500L.
  • The maximum flow rate is 2,250L/hr.
  • Recommended hose size is 2.5cm.
  • Universal hose fittings.

Our recommendation

The Blagdon 5W Mini-Pond UV Clarifier is a good choice if you have a small decorative pond that has the usual green algae problem.

5. Hozelock 1559 1240 Vorton 11 UVC

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Hozelock Vorton 11 UVC Lamp

The Hozelock 1559 1240 Vorton 11 UVC is almost the “smallest” pond UV clarifier in this review. The 11W bulb unit handles ponds up to 4,000L. This model is part of the Vorton range of pond cleaners. Your other size options include Vorton 55 UVC lamp and Vorton 18 UVC lamp (for ponds up to 6,000L).

The UV bulb is high-powered for maximum efficiency. The unit comes with a 5m power cable, the only model in this review that bothered to specify that information. And there’s a two-year warranty to stop you from worrying. Although some online reviewers remark that spare parts are difficult to come by.


  • UVC lamp that’s part of Hozelock range of Vorton UV clarifiers.
  • For ponds up to 4,000L.
  • Uses a twin high-powered 11W PLS UV bulb.
  • Comes with a 5m power cable.
  • Two-year warranty.


  • Difficult to track down spare parts.
  • Some units came fitted with a sealed continental plug that was difficult to remove.

Our recommendation

The Hozelock 1559 1240 Vorton 11 UVC pond clarifier is a good choice if you are already a fan of Hozelock garden equipment. And perhaps have invested in other pieces of pond equipment for your pond system.

Buyer’s Guide

Many people are unsure about the purpose of a pond clarifier. After all, doesn’t the pond filter get rid of all the unwanted matter in the water? This Buyer’s Guide clarifies what a UV clarifier is, how it works and what size you need to buy.

What is a pond UV clarifier?

A pond UV clarifier is a piece of pond cleaning equipment. It consists of a UV light of a particular wattage. Its purpose is to clean the water in your pond with concentrated UV light to help remove green single-cell algae (the cause of green water). This helps to keep the water as clear as crystal.

Why do I need a pond UV clarifier?

UV pond clarifiers are great for koi ponds that have heavy fish stocks

You may notice that the water in your garden pond looks a bit murky. Perhaps you can’t even see down to the bottom of the pond anymore. Much of the murkiness is caused by green single-cell algae flowing in the water. It’s difficult to remove the algae as it’s microscopically small. Pond filters don’t trap matter this small.

Ponds that are in full sun or partial shade are particularly susceptible to this problem. If your pond is in full shade, you may not need a clarifier along with your filter to keep your water clear.

Note that the UV clarifier only handles green algae. It does nothing about the long strands of weeds – blanket weeds – often found in ponds.

How does the pond clarifier work?

A UV light clarifier consists of an outer tube with a smaller crystal tube inside. The crystal tube contains a UV light. Water flows through the outer tube around the crystal tube and out the other side of the unit.

Your water pump pumps water past the UV light whose radiation destroys the DNA of the algae in the water and so kills it. The dead algae clump together and are drawn into your pond’s filtration unit or drop down to the bottom of the pond.

Where does the clarifier fit in with the pond filtration system?

Pond water should flow through a pond UV unit under pressure. And you want your filtration unit to pick up the dead algae. So the order of your pond’s units is pump followed by UV clarifier followed by a filter. This is the generally accepted view, though others say to place the clarifier after the filter as you don’t want any large debris reaching it.

What kind of wattage should I get for the bulb?

The wattage of the UV bulb depends on four things:

  • The size of your pond
  • Whether it’s in full sun, partial shade, or full shade
  • How fully stocked it is with fish
  • The maximum flow of your pump

The larger the pond, the higher the wattage of your bulb. The more sun your pond receives, the more algae you’ll have and so the higher the wattage of your UV bulb. And the more fish you have, the more algae grows and the more powerful the UV bulb should be. The flow rate of your pump determines how long the water comes into contact with the UV light.

Information about each pond UV clarifier usually contains at least the size of the pond it can cover and the maximum flow rate of the pump needed. The other information is not always readily available.

The general rule of thumb is that you need about 10W for every 3,000L of pond water for clarifying your pond.

How often do I need to change the UV bulb?

Even though your UV light is still putting out visible light, it may not be functioning effectively enough at killing algae. The useful lifespan of a UV bulb is around 10,000 hours. Beyond this time, the UV radiation it emits begins to diminish.

If you run your UV clarifier year round, 10,000 hours lasts about a year. Perhaps change the bulb in the spring when you start to get your garden ready for the growing season.

Final Conclusion

You need to be patient when using a pond UV clarifier as it can take days or weeks to get all the green algae out of the pond. But it’s worth it for sparkling clear water. Many of the clarifiers we review in this article come in different wattages, so there’s a choice whatever size and situation your pond is in.

My Best Pick is the AllPondSolutions Stainless Steel Aquarium & Pond 55w UV Light Clarifier. This is for large ponds and has a built-in thermal protection feature to prevent overheating.

My Runner up is the Evolution Aqua evo25 UVC. This model comes in a range of sizes for small to medium-sized ponds.

The UV clarifier is only one part of your pond cleaning system. I have reviews for the other pond equipment you need. Please read 5 Best Pond Aerators – Oxygenate the Water Easily, the 3 Best All In One Pond Pump and Filter Units – My Top Pick For, and 7 of the Best Oxygenating Pond Plants For Water Health and Clarity.

Last update on 2024-04-11 / Affiliate links / Images from Amazon Product Advertising API

Welcome to my site, my name is John and I have been lucky enough to work in horticultural nurseries for over 15 years in the UK. As the founder and editor as well as researcher, I have a City & Guilds Horticultural Qualifications which I proudly display on our About us page. I now work full time on this website where I review the very best gardening products and tools and write reliable gardening guides. Behind this site is an actual real person who has worked and has experience with the types of products we review as well as years of knowledge on the topics we cover from actual experience. You can reach out to me at john@pyracantha.co.uk

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