Choosing a UV Filter

The eternal question that faces every owner of the pond: “How to choose a UV filter for the pond?”. 

Which UV filter is better to choose, which company, power, with what characteristics? Let’s figure this out. 

Today, most people want to see ponds on their estates, not trivial pools. 

After all, your own pond is not only an incredibly beautiful element of landscape design but also the opportunity to live in harmony with nature, relax your soul without leaving your home.

But it’s not so easy to enjoy harmony with nature if your pond is not clean and well maintained, without proper care, it will simply turn into a nursery of fungi, algae and other parasites from which all life in your pond can suffer. 

In order for you to always enjoy clean water in the reservoir and of course its inhabitants, you need to adhere to the most important rule – to filter the water in a timely manner. 

For this, special devices have been developed that support the natural biological, transparency of water, the health of inhabitants and the cleanliness of your pond.

UV water filters are hollow chambers through which the pond water flows. 

The chamber is a UV lamp, which irradiates the water with high concentrations of UV light. 

This highly reactive light spectrum kills bacteria, which makes the water clean and destroys suspended algae. 

Ideal for problems with the so-called algal bloom. The UV filter is switched last in the filter circuit (behind the pond filter).

Choosing a UV Filter


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How to choose a pond filter

Today, the market offers a wide range of various systems for filtering pond water. 

These systems differ from each other by many criteria, for example, by the company, country of manufacture, the principle of operation, power and other parameters of no small importance. 

The issue of selecting a filter for the pond must be dealt with during the design of the reservoir itself, taking into account factors such as:

  • the depth and size of the pond
  • climatic conditions
  • Lighting
  • the presence of vegetation and fish
  • degree of pollution of the reservoir


What is a UV filter 

In a UV filter, the pond water is passed by a lamp that emits ultraviolet light. The light kills many harmful organisms such as algae. 

Algae and other organisms make your pond a green broth. 

Especially if you have a pond with lots of fish. 

A UV filter is ideal to keep your fish pond, but also swimming ponds and mirror ponds to permanently clean and clear.


How does a UV filter work?

A UV filter is actually not a filter, but a supplement to the existing filter technology. The pond water is led along with an ultraviolet lamp. 

This sterilizes the water and kills algae, germs, and fungi. 

Especially suspended algae. And that at a very low contact time. 

This means that the flow rate of the water can be high. The lamp, the UV unit, is in the first filter phase.


The purchase of a UV filter

UV lamps must be present when starting the pond. 

This is because if the suspended algae have spread over a large area in the pond, a UV filter will not be able to quickly remove these algae. 

It is recommended to keep the UV filter on continuously from the beginning of April to the end of October.

A UV unit must always be operated in combination with another filter. 

Always make sure that the UV unit has a circuit breaker. 

In this way, you avoid contact with the harmful radiation during maintenance work. 

For an optimal effect, it is important that you renew the UV lamp every year. 

Then you have a clear pond throughout the pond season.

Always pay attention to the strength of the UV lamp.

The rule of thumb for the strength of a UV filter is 2 to 3 watts per 1,000 liters of pond water.


Why do you need a UV lamp on the pond?

Above all, the UV lamp kills the suspended algae, which provide the well-known “green water” in the pond. 

When the algae is killed, they end up as fine mud and debris in the filter. 

This already answers the question of whether the UV clarifier must be connected before or after the pond filter. 

The UV pond light is always installed in front of the filter system. 

If you connect the clarifier after the pond filter, the dead algae land in the pond. But we should avoid that.

In addition, the UV algae clarifier can kill mold spores, germs, pathogens and harmful bacteria in pond water. 

Certainly, the UV device kills our pond bacteria, but this is not bad. The UV lamp is connected before the filter and not afterward. 

Therefore, these bacterial strains, which spread in the pond filter plant, also settle in the pond at the bottom.


Which UV lamp size you should choose?

Unfortunately, it often happens that the UV lamp is either too small or too large. 

If the UV lamp is too small, the suspended algae that cause green water will not be killed enough and the water will remain cloudy. 

But if the UV lamp is too large, the power consumption increases and the water hardness decreases. 

UV light softens the water. In this case, you would then have to harden the water again, with care products to water hardness.


Which UV power at which pond size?

  • 5 watts to 11 watts of power are rather something for the aquarium or very small pond from 500 to 1000 liters of water.
  • From 18 watts to 24 watts of UV power you can work with a pond size of up to 5000 liters of water.
  • For ponds over 5000 liters to about 15000 liters you should use at least 30 watts of UV power.
  • If the pond has more than 15,000 to 50,000 liters of water, we should definitely work with 36 watts of UV power.
  • For ponds with little fish stock and 55 watts of power, for ponds with lots of fish (especially koi)
  • For ponds with more than 50000 liters up to 150000 liters, we can start the experiment, first with a 75 watt UV lamp to start, then the power would be too low, we can operate a second UV lamp with 75 watts of power in parallel
  • If the pond has over 150000 liters of water, you should definitely work with 2 UV lamps with 75 watts from the beginning (connected in parallel so that the flow speed of the pond pump is halved and thus more intensive clarification is possible)


In any case, you should prefer a parallel operation to feed a 150 Watt UV lamp with a 12000-liter pump. 

The water runs much too fast through the UV clarifier. 

So use two smaller UV lamps next to each other to achieve a flow rate per lamp of around 6000 l/h. The pond hose is best selected with 32mm. 

In front of the two UV lamps, divide the hose into 2 wires using a T or Y piece. 

These can be found with the matching hose nozzles in the shop.


The construction of a UV filter

The construction of a UV filter is basically quite simple and logical. The UV lamp consists of the housing in which the light bulb is located. 

The bulb is protected from water by the quartz glass. In the case, therefore, comes first the quartz glass in which the bulb is located. 

The transformer is connected to the socket by a cable. 

Here the current flow for the UV lamp. Depending on the model or UV lamp manufacturer, the transformer can also be located directly on the housing. 

For the UV clarifiers from Sera Pond, the transformer (ballast) is e.g. installed in the lamp base. Everything has its advantages and disadvantages.

The O-ring seals protect the electrical system from water. In the housing, the water can now run from one connection to another without coming into contact with the electrical system. 

You could see that there was a short circuit if the sensitive quartz glass were broken or leaking. Therefore, you must always examine the quartz glass before each use. 

If it is broken (possibly by the parcel delivery), you must immediately inform the respective dealer, before you use the device! 

Otherwise, there is a short circuit because the water is then no longer kept away from the electrical system by the quartz glass.


What is a quartz glass and what do you have to consider?

The quartz glasses for UVC lamps are also named as follows:

  • quartz glass
  • flaskquartz glass
  • bulbglass 
  • tubequartz glass tube


In most cases, the quartz glasses are shaped like a “test-tube”. 

This means that they are open on one side and closed on the other side. 

These are the so-called quartz glass pistons. 

In some models, the quartz glass is open on both sides. 

These glasses are then called a quartz glass tube. 

The reason for this is that a fluorescent tube is used which has a contact (socket) on both sides. 

This is also called a TL socket. The other bulbs, with the pedestal on one side only, are called PLS or PLL.


Power of the pond pump to the UV lamp

It is extremely important that the water does not run too fast through the UV-C clarifier so that it is irradiated intensively enough. 

This has been proven many times by people who first went into a 36W UV lamp with a 12000 l / h pump. 

The water remained murky. But if the pump capacity was then throttled to 6000 l / h, it took only a few days until the water was clear. 

This also gives the answer to the frequently asked question, how often does the pond have to be circulated per hour? 

The criterion of the circulation per hour is absolute nonsense and has nothing to do with a clear pond. 

It is important that the water runs as slowly as possible through the UV lamp and thus remains in the pond filter for a very long time to clarify. 

Depending on the size of the pond, the water should always remain in the pond filter for at least 10 minutes so that the bacteria can “treat” the water long enough. 

And we only achieve that with a large filter volume and small pond pumps. If you e.g. 

take the Sera Pond PP 6000, which has 6,000 l / h of rated output, you can go out after deduction of the pumping height of about 4000 l / h. 

Large pond filter from 4 rain barrels to 50000 liters, has a capacity of 1200 liters. 

At this pumping capacity, the water would then be in the pond filter for approx. 18 min. That’s perfect!


Does the UV lamp harm the bacteria in the pond?

Does the UV lamp harm the bacteria in the pond?

No! The bacteria are produced in the pond filter. In the pond, the bacteria then settle on the pond bottom. 

This is only possible if the UVC lamp is installed in front of the pond filter. 

Therefore, you must never install a UV filter directly in the pond filter. 

They would kill the bacteria directly in the pond filter. 

But the UV lamp also kills bad bacteria. Even viruses and mold spores are destroyed by UV radiation. And that’s a good thing, as it prevents fish diseases.

You should now know how to connect the UV lamp to the filter so that no damage is caused by the UV lamp in the pond. 

If the suspended algae are to be killed, you must also use the UV lamp. This is far better than destroying the algae with chemicals.


The UV lamp does not shine

If you can not see any light in the UV lamp, it probably will not shine. 

That means there is a defect somewhere. Now you have to determine where the error comes from. Here we list the most common sources of error:

The light bulb has burned out or is not shining at the beginning. 

Therefore, you should always buy one or two UV replacement bulbs for each UV lamp in order to perform a bulb damage check. 

If you do not have a spare lamp on hand, you can only guess. 

You have to change the bulbs every season anyway. 

So be sure to cover yourself with UV replacement bulbs when you buy them.

You are trying to test the UV lamp when it is removed. It is often forgotten that the devices have installed depending on the manufacturer, so-called micro-switch for bridging. 

This is to prevent you from looking into the bulb. 

Do not look directly into the UV radiation, as this is harmful to the eyes. The microswitches are often on the side of the socket. 

The quartz glass is broken and the electrical system burned out due to a short circuit. 

Therefore always check the quartz glass before each use and again after a few weeks. 

Finally, you have to clean the quartz glass again and again.

The power source to which the UV lamp is connected is faulty. 

Even thunderstorms can cause over-voltage to burn out the bulb.


How often do you have to change the UV lamp?

The UV lamps last for an average of up to 6 months with the killing effect. That means from spring to autumn. This means that you should change the UV lamp or the light bulb once a year.

After 1 year the bulb has to be replaced. Although this shines like a normal household light bulb but has no killing effect. This means you are just wasting power without making an impact.


Replacing the UV lamp

When replacing the bulb, be careful to only touch the bulb at the base, as grease stains on the glass surface may affect its life. Pull out the old bulb and insert the new one. 


Do you need a UV filter in winter?

Due to the many ice damage caused by UV lamps in winter, we recommend not to operate the UV lamp in winter. 

Only a small amount of ice on the quartz glass is enough to break the glass. 

If you switch the UV lamp on again in the spring, you should buy a new transformer unit because of the water damage and short circuit.

You can operate the pond filter already in winter, but then without a UV lamp. 

The formation of algae in winter is not so huge and you can even do without the killing UV effect. 

Store the device in the basement. Disassemble it into items such as housing, quartz glass, and electrical unit. 

The electrical system should be stored dry. 

In the spring you rebuild the UV lamp and put the pond filter into operation as usual.

Types of pond filters

Let’s now take a closer look at what types of filters are:

  • Pressure filter – their feature is that it can supply purified water above the level of its location. After undergoing filter cleaning, water can be used for a cascade fountain or a small stream.
  • Flowing (external) filter – these types of filters are installed on the shore of the garden plot. With such a filter, water simply flows down.

types of pond filters

Pressure Filters:

Today pressure filters are considered the most convenient in operation, as well as economical. 

This type of filter is designed to clean small ponds. The essence of this device is very simple, under pressure it passes water through itself, water, in turn, it passes through various degrees of filtration. 

If the filter is equipped with a UV lamp, then the water is further disinfected using UV rays to sterilize the water. 

The advantage of this kind of filter is that it can easily be masked, but the disadvantage, unfortunately, is the constant need for a large head of water.


Flowing Filters:

Flowing filters are designed for cleaning large volumes of water up to 200 m3 (cubic meters). These filters are a kind of reservoir with all the filter elements necessary for cleaning the pond. 

This type of filter is already installed above the water level in the reservoir. The main and indisputable advantage of such filters is precisely their long service life and, of course, high performance. 

Flow filters have only one drawback, it is not possible to mask it, but this is a completely unimportant drawback.

So, in order to clean the surface of the pond water, we recommend the use of special devices, such as “Pond Skimmers”. 

The role of this device is very important when cleaning a reservoir. 

Skimmers also exist in two types of floating and built-in. Skimmers will remove all large particles (grass, leaves) before they sink to the bottom and contaminate the body of water. 

The device is very easy to use, does not require time-consuming to clean the wastebasket itself. 

Debris from the skimmer basket can be removed without additional dismantling of the device, simply by removing the basket. 

The water quality in your pond directly depends on the performance of the skimmer.

But let’s not forget that in addition to filtration, for the ideal state of our pond, we need additional elements, such as:

  • Pump for the pond
  • Compressor for the pond
  • UV pond sterilizer
  • Pond chemistry
  • Food for pond fish (if they are of course present in your pond)
  • Pond heaters
  • Fixtures for the pond

Why are these elements necessary? So let’s look at why each of these elements is necessary.


Pond pump:

A pond pump is an indispensable attribute for everyone who has a pond. 

The main function of the pump is precisely the fast and most importantly almost silent pumping of water into the pond. 

The convenient, stylish, outsized design makes it possible to disguise it as conveniently as the landscape design of your pond.

Pumps are an indispensable tool for filtering water in your pond. 

Modern pumps for ponds have high performance, power and keep pace with technological progress. 


Compressor for the pond:

It is a necessary and integral part of your pond. 

The compressor will provide the necessary oxygen to the plants and fish of your pond. Pond compressors have increased productivity and power. 

They are quite resistant to environmental influences (climatic conditions).


UV sterilizer for the pond: 

It will become you an indispensable assistant in the destruction of unwanted algae in the pond, as well as destroy the green water, thereby making it transparent and healthy. 

That is, sterilizers are necessary in order to keep the water of your pond clean without harmful microorganisms.


Pond chemistry: 

Necessary to ensure that the fish in your pond develops properly and is healthy.

If you do not have a sterilizer but you have water “blooming”, you can choose a wide range of drugs and cure water.

With the help of drugs, you can easily achieve remarkable results when breeding fish in your pond, without applying any special effort. 

If you have found any diseases in fish, you can easily find a suitable drug on the market. 

All preparations are aimed at creating the most favorable and optimal conditions for the inhabitants of your pond.


Food for pond fish:

In addition to basic care and water quality, fish still need healthy and proper nutrition. 

It is very important to choose an optimally balanced natural diet for pond fish is the key to the growth of your pond inhabitants. 

Be careful when choosing a diet and consider factors such as the type of your fish, weight, essential minerals and vitamins.

Make sure not to overfeed your fish, as this leads to higher ammonia levels in your pond, and your pond can suffer greatly.


Pond heater: 

Installing a pond heater is necessary to ensure that your pond pleased you not only in the warmer months but also on colder winter days. 

Recently, the use of pond heaters has become very popular. 

The main way to use them in ponds is, of course, to control the temperature differences of the pond in the cold season. 

The pond heater prevents the freezing of water in the winter and maintains the temperature of the reservoir unchanged, thereby not injuring the inhabitants of the reservoir in case of temperature changes.

Also, heaters are necessary for those people who are engaged in the breeding of heat-loving species of fish. 

Be careful, regardless of the purpose for which you use a pond heater, you should carefully approach the issue of its choice. 


Fixtures for the pond: 

These are an important part of the landscape design of your pond. 

In order for your pond to look fantastic while playing with different colors, pond lights are what you need.

Pond lights are of two types, ground and underwater. 

You can add sophistication to your pond by highlighting its individual parts both from the outside and from the inside. 

Blue, green, yellow, red colors will create a unique and unforgettable image of the pond and add sophistication. 

Most underwater lights have several color filters, so you can change the color to your taste and desire.

Now you know what appliances are needed to ensure that your pond is not only clean, but also beautiful, and its inhabitants feel as comfortable as possible in it.