Air pumps for fish ponds

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Last updated 2nd June 2014
Adding life-giving oxygen to your pond is easy with air pumps.

Why aerate a fish pond with an aerator?
Running an air pump for a fish pond
Which air pump for a fish pond?
Fishpond air pump maintenance
Eleven tips for buying and using fishpond air pumps

Why aerate a fish pond with an aerator?

Koi and airstone bubbles

In addition to needing dissolved oxygen to breathe, Koi and other fish are dependent on filters and their bacterial inhabitants for detoxifying their waste products. These processes also require oxygen, and the more active the fish, the more active the filter bacteria need to be.

During warm weather, oxygen is also more in demand as pond plants grow vigorously, using up oxygen at night.

Any pumped water exposed to air will become aerated to a certain degree, so pumps for filters, fountains and waterfalls contribute air, working quietly and continuously to keep your pond’s inhabitants healthy.

But air pumps are dedicated to pumping air directly into the system, usually via an airline and airstone. Keeping the air pump constantly running gives peace of mind as it provides temporary backup if the filter pump or aeration devices fail.

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Running an air pump for a fish pond

Unlike venturis (either stand-alone or supplied as part of a filter unit), air pumps require a power source; usually electricity from the mains.

Air pumps (from Bradshaws Direct and Pondkeeper) move a small amount of air at high pressure and speed.

One effective way to use them is to drive air through one or more airstones (perforated balls of rubber, sponge or ceramic) or membranes to create thousands of air bubbles deep in the pond. This is an ideal way for oxygen from the air to dissolve in the water, providing essential aeration.

However, the amount of dissolved oxygen achieved depends on the water temperature in your pond.

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Which air pump for a fish pond?

Models and prices vary, as well purposes and performance (specified as litres per minute of airflow).

For general fish ponds, you just choose the right pump for a particular pond volume (see Bradshaws Direct and Pondkeeper). Complete kits come with with one or two outlets, a length of silicone airline tubing, and one or two airstones. Spares kits are usually also available.

For more demanding ponds containing Koi, you can’t have enough oxygen and must be sure not to overstock your pond and risk fish dying. Seek suitable units that pump out more air than those for general ponds and consult Koi specialists such as Absolute Koi for advice on the airflow rates. Browse units from Pondkeeper and the various Koi specialists.

Most air pumps are fitted with rubber diaphragms, but the Medo range (from koi care specialists such as Little Bigpet) uses more reliable pistons instead. These pumps are quiet, compact, efficient, long-lived (10,000 hours life expectancy), oil-free and easily maintained. They are designed to pump to ponds 2m deep and are available in three sizes, with outputs from 28 to 120 litres per minute.

Not an air pump, but an airstone, the Oxytex from Oase is an interesting accessory designed to attach to any pond pump, including Oase’s solids-handling Aquaoxy and Aquamax range (view these at Pondkeeper). The airstone sits on the base of the pond, with its green fronds designed to mimic a plant and blend in as much as possible.

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Fishpond air pump maintenance

Air pumps are designed for long life and low maintenance, but benefit from routine checks once isolated from the mains supply.

The most important routine task is to check the air filter and clean or replace it as necessary to prevent wear on the diaphragms. New filter foam is easy to cut to size. Airstones may also clog up with algae and cause potentially pump-damaging back pressure, so need cleaning or replacing. Some airstones will erode eventually to the point of uselessness, so replace them at intervals.

Ceramic airstones, unlike rubber or sponge airstones, are a good long-term option. They do not clog and give a better distribution of air with finer bubbles than other types of airstone. Spherical and cylindrical shaped airstones are also available in a range of sizes.

If the pump becomes noisy, check the diaphragms for splits or other wear, and replace accordingly.

And last but not least, check that all connections are sound in all your electrically-powered equipment, and be sure to replace damaged cables (ensuring you use outdoor cables).

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11 tips for buying and using fishpond air pumps

  • Decide what depth you need to pump air to, and how many airstones you want to install.
  • Consider using more than one air pump for the right aeration.
  • Remember air pumps and the mains connection require a dry, weatherproof chamber.
  • Browse pond suppliers’ catalogues to see what’s available (eg Bradshaw’s Direct and Pondkeeper)
  • Choose a pump with easy access to the air filter.
  • Look for a long life expectancy.
  • Check that the soundproofing is sufficient to avoid disturbing your neighbours.
  • Fit above the pond’s water level to avoid back-siphoning if the pump stops running.
  • If the pump has multiple outlets, blank off any unused ones to stop loss of pressure.
  • Install airstones in the transfer ports of the filter chambers so media isn’t disturbed by streams of bubbles. This ensures that all water flows through the media.
  • In winter ensure that airstones in the pond are positioned at least 30cm above the pond’s base, so that the denser, warmer water isn’t disturbed and cooled.

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