Pond pumps & filters

Pond Pumps, Filters and UV Clarifiers
There are three essential pieces of pond equipment needed to ensure that your pond is a clean and healthy environment for your garden fish to live in.

1. Pond Pump.
2. Biological Pond Filter /Biofilter.
3. UV clarifier/UVC/UV Steriliser.

The main objective of the pond pump is to circulate its water through a filter and to provide oxygen to your garden fish. This process prevents the pond from becoming stagnant and removes all solid and soluble waste. Pond pumps are also used to run streams, cascades, waterfalls, fountains and spitters.

There are two types of pond pump available.

Submersible pump
This is the most popular pond pump available as it is adaptable to the size of the water feature you wish to create, from the smallest fountain to the largest waterfall. It is also easy to install.

External pump
This type of pump, as its name suggests is positioned outside the pond. The pond water is drawn through a rigid suction pipe and pumped through an external filter. This type of pump is more suited to larger or commercial style ponds.

Things to consider when purchasing a pond pump

  1. Type of garden fish you wish to keep. Koi ponds will require more water turnover than a goldfish pond.

  2. Volume of pond water. Pumps are sized by gallons of water pumped per hour (GPH).Some companies label pumps by GPH while others assign letter or number designations that require cross-referencing to charts. To determine the correct submersible pump for your pond, you should determine your garden pond’s volume. It is recommended that you circulate your pond’s water once at least every 2 hours. Therefore your pump should have a GPH (gallons per hour) rating of at least half of your pond size.

  3. Type of water feature you wish to achieve- eg a fountain will require a pump with a higher pressure than one designed for a small water feature.

  4. Efficiency of the pump. As your pump will be running 24 hours a day, 7 days a week, power consumption is a big consideration. Many people choose a pump based on its cost. It may seem appealing to buy the cheapest pump. However the running costs are often higher, making it false economy.

  5. Choose a pond pump from a well known manufacturer with a proven track record. Pumps from leading manufacturers are designed to last for long periods and have excellent warranties.

A pump is a crucial part of a pond system and it is vital that it is purchased with a specific pond volume and head in mind.


A filter box is essential for cleaning your pond water. To ensure your filter is functioning to its maximum capacity it must run for 24 hours a day, and be connected to a pump of the right size for your pond.

It is a myth that a filter works by removing physical dirt and this keeps the pond water sparkling clean. Sadly this is not true, although a small amount of waste will be strained from the pond as it passes through the filter. The most important purpose of the filter is to act as a mini sewage system for the pond. In simple terms the media within the filter creates a huge surface area, which becomes home to many millions of helpful bacteria. When fish waste, excess food or decaying organic material fall to the bottom of the pond it starts to break down and release toxins into the water. As the water passes through the filter the helpful bacteria break down these invisible toxins and any other organic waste which get caught up in the filter. Clear water does not mean healthy water.

Therefore it is essential to buy a filter, which can easily cope with your pond volume and garden fish stock. You need to know the volume of your pond to 80% accuracy if possible. Also consider that your garden fish will grow, and as they do they will produce more waste, so always opt to buy a filter that is bigger than required. If you are intending on keeping a large koi pond, it is better to purchase a combined UV and filter for cost purposes.

Size of filter required

Goldfish – the volume of pond water should be filtered every 2 hours.

Koi – the volume of pond water should be filtered every hour.

Pump and Filter Sets
These pump and filter sets work out cheaper than if you had bought a filter and pump separately. You can also guarantee they are compatible as they will be have been made by the same manufacturer.

All in One Systems

This consists of a pump, filter and UVC unit. It is very easy to install and all of the equipment is hidden under the water.

Different types of biological filters

Gravity Return Filters.
These filters are pump fed with gravity outlet. These will require a pump in the pond that feeds the filter. Water will then simply pass through the filter and return to the pond under gravity. This means the filter outlet must be higher than the point at which you want the water to return.

Pressure Filters
Pressure Filters are ideal for small to medium size ponds and are directly fed from a pump in the pond. However since the filter is a sealed unit the water is still under pressure when leaving the filter, allowing much more flexibility in the positioning of the unit.

Gravity Fed Filters
Gravity Fed Filters are ideal for larger Koi ponds. They are complex units to install and expert advice is required.

It is impossible to have a filter too big for a pond and Koi ponds should have the biggest filters of all.


A pond UV clarifier is an electrical unit which water is pumped through before it reaches the pond filter. Its purpose is to kill algae cells by attacking them with UV rays, causing them to clump together therefore making it easier to remove either by your filter or pond vacuum if you have one. A UV clarifier only works in conjunction with your ponds biological filter.

The purpose of the UV clarifier is to control the build up of algae in the pond. Other methods of controlling algae include introducing pond plants, building your pond in a shaded area or using pond algaecides. Pond algaecides are not a wise choice if you have garden fish in your pond as they can be potentially dangerous to the fish. Therefore the best method to avoid green water permanently is to use a UV clarifier. Using this process holds several advantages including easy installation, it doesn’t interfere with the chemistry of the water and it causes minimal stress to your garden fish.

Algae have some beneficial uses to your garden fish as it is a valuable source of nutrients particularly to recently hatched fry. However, green water which is caused by floating algae bloom stops you from being able to see your garden fish which could have disastrous consequences if there are sick or injured fish in your pond as they can not be seen properly. Also at night time algae respires causing the levels of carbon dioxide to rise along with the waters pH level. Such variations in water quality cause your garden fish to suffer with stress. The fish in the pond will have to compete with the algae for oxygen and can cause fish to suffocate.

The combination of using a filter which removes toxic ammonia and nitrates from waste and the ultra violet clarifiying process is very effective and maintains a beautifully clear sparkling pond which your garden fish will flourish in.
Using a UV clarifier will cost less money in the long term not to mention time and effort in controlling algae.

Considerations when choosing a UV clarifier for your pond

  • It is impossible to have an UV clarifier too big for your pond.
  • If your pond is shallow, pick a larger unit.
  • If your pond is exposed to full sun with no plants, again pick a larger unit.
  • Ensure the unit can cope with your desired flow rate.

Consider purchasing a combined biological filter/UV clarifier system. You will need to ensure that BOTH functions are compatible to your ponds needs. A combined unit is simpler to install than separate units and has less plumbing.

The section on pond maintenance explains what checks should be carried out on your pond pump and filter throughout the year.