Protein skimmers (foam fractionators) for fish ponds

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Last updated July 2014
Koi keepers enjoy watching their fish, but it’s not possible if there’s foam on the surface.

Foam and scum problems in Koi pond
What causes foam and scum in fish ponds?
How to keep fishpond foam at bay
Can protein skimmers control fishpond foam?
Why buy a protein skimmer?
Maintenance of a protein skimmer (foam fractionator)
Ten top tips for choosing/using a protein skimmer

Foam and scum problems in Koi ponds

Copyright (c) Alec Scaresbrook. Keep a foam-free pond.

You’ve probably seen foam on the surface of rivers and streams, in the pools at the base of waterfalls and weirs, or by canal lock gates.

Unless your Koi are living in a sterile environment, you could come across foam and soapy scum problems in your pond too, particularly where water is turbulent. Read on to find out how to keep the pond crystal clear, like the one in this photo.

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What causes foam and scum in fish ponds?

When you see unsightly yellowish water, oily-looking scum or frothy layers on the surface of the water, it’s easy to think of pollution from detergents. But more often it is due to air bubbles that take so long to burst that they float around on the surface of the water forming a raft. Bubbles are a sign that there’s plenty of air being introduced into the water by a venturi, fountain or waterfall, and, in moderation, these extra long-lived bubbles aren’t harmful to your Koi, they’re just unsightly.

The long life of the bubbles is because of dissolved organic carbon (DOC) in the water. This broad term covers any chemical compound containing carbon. Fish waste also increases the DOC levels as well as decaying food and plant debris.

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How to keep fishpond foam at bay

It’s not just Koi keepers who have this problem of dissolved organic carbon – marine aquarists have also faced this problem, and come up with an answer – a foam fractionator (also known as a protein or foam skimmer).

This piece of equipment creates many tiny bubbles which attract organic carbon compounds to their surfaces as they rise through the water. By controlling bubble formation the resultant foam can then be skimmed off the surface and removed from the system.

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Can protein skimmers control fishpond foam?

The size of the bubbles produced is critical to success. The right size bubbles to trap dissolved organic carbon (DOC) in fresh water have been hard to create artificially, despite them forming so readily where they’re not wanted.

It’s only recently that equipment has been available to freshwater fish keepers. These clever pieces of kit work on the same principle as the marine equipment, incorporating a venturi to create bubbles in a controlled manner so that they can be separated from the pond water and easily removed before there can be a build up of discolouration, scum or foam in the pond. As a bonus, because foam fractionators remove excess DOC, they effectively reduce plant nutrients so algal levels can be reduced too.

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Why buy a protein skimmer?

Some Koi specialists consider that feeding the right formulation of food in the right amounts is enough to prevent dissolved organic carbon (DOC) becoming a big problem.

After all, uneaten food and all the waste generated by the fish after eating the food contributes significantly to the DOC load. But it can be difficult for newcomers to the hobby to get this balance just right, and some long-standing fish keepers find it difficult too.

It’s very hard for hobbyists to gain the amount of experience of Koi dealers, and, unlike dealers, they aren’t always able to give 100 per cent of their time to tending their Koi, judging the water quality and adjusting conditions.

So if, after all your efforts, you still have scum and foam problems, there’s no shame in resorting to equipment to make your hobby more satisfying. With a foam fractionator to deal with the excess DOC levels, you’ll have more time to enjoy watching your Koi. Many specialist Koi dealers either stock or can order this equipment.

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Maintenance of a protein skimmer (foam fractionator)

There’s very little to do other than monitor the waste container and occasionally flush out the pipework with a hose.

You’ll also need to give the pump a regular service, but fortunately a pump problem won’t produce the crisis that a filter pump failure would.

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10 top tips for choosing/using a protein skimmer

For a clear pond surface:

  • Remember that a protein skimmer (foam fractionator) cannot replace a good filtration system, it just supplements your set-up.
  • Ask Koi keeping friends and dealers for their opinion of the different protein skimmers (foam fractionators) available.
  • Do not fit the protein skimmer (foam fractionator) inline with your filtration system. Fit it as an accessory running off its own pump.
  • Check the manufacturer’s recommendations for make and model of pump. And make sure that you set the pump to run at the recommended flow rate.
  • As ever, be aware of electrical safety when connecting the pump. Use a residual current device and get advice from an electrician if you have any doubts about the installation.
  • Always fit the unit above the surface level of the pond to avoid any back pressure problems.
  • Return cleaned water to the pond or to the final chamber of your filter system.
  • If you direct the waste to a container, make sure you empty it regularly to avoid it overflowing.
  • Use the waste for garden fertiliser. Store it as a concentrate and dilute it when needed before watering garden beds, borders and containers.

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