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Floating Fountains & Dam Aerators

Floating Fountains and Aerators for Dams, Lakes and Large Ponds

Pond Help & Information

Need a hand working out the right gear for your project? Browse our range of help pages or submit a help request directly to our specialists.

Pond FAQ

1.       Why has my pond water turned green?

If the water is green it is caused by Green Water algae (or Pea Soup algae), Green water algae are microscopic single cell plants that multiply rapidly when conditions are suitable. The algae will flourish when there are excess plant nutrients in the water e.g. nitrate and phosphate and excess sunlight to fuel their photosynthesis. As well as being unsightly this algae can cause potentially lethal changes in the water pH and oxygen levels. The algae must be controlled and there are several ways of doing this. For further information – green water

  • Increase the stock of pond plants to out compete the algae for plant food.
  •  Encourage plant growth to cover about 2/3rd of the pond surface to reduce sunlight.
  • Pump the water through an Ultra Violet Clarifier (UV-C) which kills the algae and clumps it so that it is caught in the filter. Do not use a UV-C in a new pond for at least 6 – 7 weeks so that the beneficial bacteria can colonise the filter pads.
  • If it is a new pond add some Interpet Bio-Start  to promote the establishment of beneficial bacteria. It will take up to about seven weeks for the pond to achieve balance.
  • Treat the pond with Interpet Green Away to kill off the algae and then regularly dose the pond with Interpet Extract of Barley Straw.
  • Check that there is sufficient water movement and fit a larger pump and filter if necessary. The pump should have sufficient capacity to turn over the total volume of the pond every 2 hours
  •  Once the algae has been treated dose the pond with Interpet Sludge Buster to break down the dead algae.

2.       Why are the edges of my pond turning green?

Fibrous green strands of cotton wool like algae called Blanket Weed or String Algae, which if allowed to grow unchecked, will choke the pond. Blanket weed grows by utilising excess nutrients in a pond and can rapidly choke plants and equipment and make the pond look unsightly. Be careful to use blanket weed treatments that have been especially formulated for garden ponds as these will have no detrimental effect on the pond eco system. Treatments such as Interpet Pond Balance and Blanket Weed Algaway are formulated for pond use and are safe. To control blanket weed the procedures used for green water algae will also work for blanket weed, with the exception of the UV-C which has no effect. For further information Link to Blanket Weed / String Algae


3.       Why do I have to run my pump continuously?

The pond water needs to be circulated continuously to maintain oxygen levels, prevent stagnation and when used with a filter, remove foreign particles from the water. If you have an ultra violet clarifier to control green water algae, it must run 24/7 to be effective. 

4.       Why is a filter necessary?

You have invested time and money in your garden pond and you expect to be able to see the fish, we have all heard stories about the green pond in the yard that has been ignored for a long time that, when finally cleaning it, a number of seemingly healthy fish are living in it.

For you to be able to see your fish you need clean water and for clean water you need good circulation and filtration. Filter are available in three basic types, in pond, gravity and pressure.

In-pond filters are generally simple foam blocks or trays fitted to the intake side of the circulation pump; these are suitable for the smaller pond only.

Gravity filters are particularly efficient and are generally used for large ponds, particularly those stocked with Koi; these are large, and very efficient, but the filter boxes cannot be disguised easily as they must be located above the water level so that the cleaned water can run back into the pond by gravity.

Pressure filters are fitted inline after the pump and can be buried in the garden up to their lid for disguise and the outlet can be run up and over a waterfall or creek. 

5.       How often should I test the pond water?

The water should be tested weekly so that any subtle changes in water quality can be corrected before they become a problem. Test strips by API and OASE are dipped into the water for one second then compared to a supplied colour chart; from this it is easy to make corrections before they become problems.

6.       I have a waterfall on my pond; do I have to run it continuously?

If you are using the same pump for the pond circulation as the waterfall you can divert the water so that the waterfall is run when you want it, but make sure that there is sufficient thin water (water running over rocks, sprays etc) to provide continuous oxygenation.

It is often better to have a dedicated waterfall pump which can be operated from a timer so that you can have the waterfall on when you want it.

7.       My pond has a lot of sludge on the bottom, how do I clean it?

The sludge is a mixture of decaying vegetable matter from the pond plants and algae and is effectively an underwater compost heap. As this breaks down it releases nutrients into the pond water which feed the plants and the algae. The sludge can be removed from the pond with an underwater sludge vacuum

8.       What is pH?

A measure of water acidity and alkalinity with neutral being pH 7.0, less than 7 is acid, the lower the number the more the acidity, over 7 increasingly alkaline. The acceptable range for a garden pond is between pH 6.5 and 8.5, with the ideal being pH 7.5.

If the pH falls outside this range it must be adjusted gradually by dosing the water with pH Adjuster.

9.       How do I work out the correct pump and filter for my pond?

Our web site has a lot of information on this subject which will help you to correctly size your pump and filter, see the links on either the pump or filter page and follow the links, but if you have problems you can always call us for help.

10.     How do I find a leak in my pond?

A leak can be very difficult to locate. First check that all of the plumbing, hoses, fittings, filter, waterfall or creek etc are intact. If the circulation system does not have any leaks it must be in the pond.

Mark the water level daily (or as often as necessary) and when the level does not fall lower, the leak must be at the water level. Make sure that the level has not fallen too far so that the fish and pump have sufficient water.

Once the level of the leak has been established, carefully inspect the liner/pond wall at the water level to locate the problem. Once the leak has been found it can be repaired with the appropriate patching system.

11.     What is the nitrogen cycle?

Once a pond has matured, a natural cycle will have developed which, in combination with the pump and filter, will keep the pond environment in balance. After the first six weeks beneficial bacteria have colonised the pond, these bacteria are essential as they convert ammonia from the fish waste to nitrite, then the nitrite to nitrate which is then used by the plants as fertiliser. 

Nitrogen is a vital element of protein and is absorbed by green plants in the form of nitrate. Together with ammonia, ammonium and nitrite, it is found naturally in rivers, lakes and streams in very small quantities. In a pond environment, nitrogen compounds (nutrients) can be created quickly by faeces,
urine and other excreta, plant remains and decaying food When concentrated these nutrients can have a harmful effect on a ponds inhabitants. Organic nitrogenous substances decay in stages in the presence of oxygen, a process called ‘oxidative breakdown’. It produces various nitrogen compounds (nutrients) as follows… 
Toxic ammonia and non-toxic ammonium are produced in the first stage of the nitrogen cycle. 
The pH value determines which of the two will predominate.
Ammonia occurs at a pH of 7.0 and over.
The second stage of the nitrogen cycle is nitrite which is the result of the bacterial oxidation,
or combustion, of ammonia/ammonium.
Nitrite is also toxic to aquatic life, but not as toxic as ammonia.
In the third and final stage nitrite is converted to nitrate. Nitrate is harmful only in very high concentrations. The key element and most important factor to get all of the above to work is the availability of free oxygen.

12.     Why is a pump necessary?

A natural pond with no or minimal wildlife needs a water turnover equal to its volume every two hours to keep the system healthy. A garden pond is an un-natural size and would not normally exist in nature so it needs help with a correctly sized pump and filter to keep the water clean.

13.     Why is the carbonate hardness (CH) important?

Carbonate hardness is the measure of the pond water hardness or softness and is one of the most important water parameters. The CH level stabilises the pH of the pond water and prevents any sudden changes in the pH, either up or down, both of which are equally dangerous. The hardness level must be 4° or greater, levels lower than this contribute to the formation of ammonia which is toxic to both fish and plants.

14.     What is total hardness (TH) ?

Total hardness is not an indication of the stability of the pH, this is the function of the carbonate hardness (CH). The total hardness is the proportion of the magnesium and calcium ions in the water and is essential for the health of the fish. For garden ponds the level should be between 8° and 10°.