The photo above is that of a Koi (Japanese carp). This one is a Goromo - one of the many different varieties of Koi . One of my first and certainly not my last.

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Monday, June 15, 2009

Regular Koi Pond Maintenance Tasks

Koi pond maintenance can be broken down into the following tasks.

  • Partial Water Changes
  • Filter Maintenance
  • Pond Maintenance
  • Replacing of failed parts

Partial Water Changes

Do not change all the pond water at once. Do regular partial water changes. Partial water changes are essentially to remove accumulated nitrates from you pond water. Nitrate is an output from the biological filtration system and although not harmful to the fish, a build-up of nitrates in the pond can lead to algae bloom, water discoloration (brownish tint) and in the long term harmful to the pond occupants (except for the plants!).

Filter Maintenance

Biological filtration relies on bacteria to work, so it is best to clean the filter only when needed. Filter media like filter mats, coral chips, beads, would clog after long periods of use and start to restrict the flow of water through them. When this happens, the media would need some cleaning. Depending on your filter design or filter system, back-flushing of the filter media (reverse direction of water flow through the filter) is a good way to remove accumulated dirt within the filter media. Never clean all the material or filter chambers at the same time since you need to have some bacteria for the filter to work. You may want to reduce the fish feeding for about a week after filter maintenance to allow the biological filter to re-stabilise itself. Stop the feeding completely if you observe that the Koi is listless, lying at the bottom or show other signs of distress.

Pond Maintenance

Over time debris from fallen leaves, sticks, fish waste and sludge will build up at the bottom of the pond if you do not bottom drains build into your pond design. Ponds with bottom drains will typically not suffer a built-up of such debris since the dirt is constantly being suck into the filter system. Hence pond maintenance is relatively easy or not really needed. For ponds without bottom drain system, a pond vacuum cleaner would be needed. Just like household vacuum cleaners, pond vacuum cleaners suck up the dirt from the pond where it can be disposed of, or used as fertiliser.

Algae removal may be needed, if you did not do regular partial water change or did not have a good filter system. In this case, we are referring to string algae. Algae that grow on the side of the pond are alright and the Koi loves to graze on them. Best way to remove string algae is to twirl them round a long stick, like cotton candy.

Replacing of failed parts

Pumps and electrical parts including bulbs for UV system and underwater lights do not last forever. Typically lifespan of my submersible pump which runs non-stop is about 2 to 2.5 years. When designing your pond and piping system, make sure such maintenance can be carried out easily without having to drain your pond! Have a spare pump on standby as Koi dies after a few hours without aeration.

For more information on pond maintenance equipment such as pond vacuum cleaners, check out these online stores (PondKeeper UK).


  1. What about water vacuum cleaners? Do i need to remove my fish to clean a garden pond? I've read several websites saying it totally harmful to clean with fish in it but how???

  2. I have not used pond vac myself but had seen it being used with fish still in the pond. I guess the risk is fish being suck into the pond vac by accident. I think fish will instinctively avoid the suction of the pond vac nozzle if you move the nozzle slowly in the pond while cleaning the bottom of the pond.

    1. Well it sounds pretty convincing, thank you! =)