Water purifiers for Koi ponds

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Last updated July 2014
A water purifier is essential if you live in an area with water supply that’s toxic to Koi and other fish.

Should fishpond keepers treat tap water?
Tap water suitable for humans and fish?
Water conditioners for removing chlorine from tapwater for fishponds
Water purifiers to remove chlorine and other toxins from tapwater for fishponds
Chloramine problems in tapwater for fish ponds
The problem of pure water in fish ponds
Seven top tips for choosing and using a tapwater purifier for fishponds
Range of water treatments

Should fishpond keepers treat tap water?

Koi pond in a private garden. Koi need purified water.

Most fishkeepers fill up (and top up) ponds with tap water, but tap water is hardly a natural habitat for fish. So should you be treating it to make it more suitable for your fish, especially Koi?

The answer is yes. In certain areas a purifier is the only way to make sure your water is toxin-free, but you’ll need to advice on how to treat the water correctly.

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Tap water suitable for humans and fish?

The water companies’ remit is to provide safe drinking water for humans, and the problem for fish keepers is that the treatments used to purify tap water are not necessarily suitable for fish. Additional chemicals are also picked up from the metal supply pipes, which causes more problems for the Koi keeper.

There are known fish toxicity levels for various chemicals, but persistent low levels of toxins can be just as dangerous as spontaneous high ones. Low levels of toxins take a long time to accumulate and produce obvious effects, and therefore are much more difficult and time consuming to research.

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Water conditioners for removing chlorine from tapwater for fishponds

Chlorine is one of the main problems in tap water because it’s harmful to fish at very low levels. Although some chlorine escapes when tap water is left to stand for several weeks, and some also escapes if water is added to a pond via a spray attachment, until recently the only sure way to remove all chlorine has been to add a tapwater treatment or water conditioner, such as those from Bradshaws Direct and Pondkeeper.

These conditioners bond with chlorine to make a neutral chemical compound that will not harm your fish. Always follow the manufacturer’s instructions when adding any treatment to your pond, and make sure you know exactly how much water it holds.

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Water purifiers to remove chlorine and other toxins from tapwater for fishponds

The more advanced solution to chlorine and other toxins is an inline water purifier/dechlorinator, available from Koi equipment specialists such as Absolute Koi. But, as when buying any Koi equipment, you do need to ask some pertinent questions about whether you need one, and how effective they really are.

First, you need to know what’s in your water supply, and which chemicals are potentially a problem. The simplest way to find out what’s added to your water is to ask your water supplier. But be aware that water companies adjust additives to suit the current situation, so toxin levels may fluctuate. For example, although water companies may not routinely add pyrethrum, they will add this insecticide to deal with occasional wildlife in the water. If pyrethrum is in your drinking water on the day you use it, then your Koi are in serious trouble. Similarly, a lab report on a particular sample of water can only tell you what’s in the sample, not what’s in the water at other times. So you need to provide for all eventualities.

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Which water purifier to treat tap water for fishponds?

Water purifiers are made for all sorts of applications, industrial, domestic and for swimming pools, but few were designed with fish in mind. Some purifiers only take out odours and colours to suit human consumption; others remove more compounds. Some may add substances too, and can alter the pH.

So don’t just buy any water purifying equipment from any outlet; use specialist suppliers and find out if the purifier is designed for fish keeping purposes. Choose between off-the-shelf general purifiers, and customised water purifiers based on analyses of your drinking water reports.

Whichever you buy, it will consist of a series of cartridges that the water flows through. The first cartridge is a sieve for tiny particles and parasites, and the others are designed to deal with chlorine, chloramine, pesticides and some metals. Absolute Koi are a good starting place.

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Chloramine problems in tapwater for fish ponds

In certain areas of the country, chloramine is added to drinking water as a more effective and long-lasting way of adding chlorine.

The compound slowly releases chlorine and ammonia, both toxic to Koi, and if chlorine is removed from the water, the chloramine then releases more in response. So if you see chloramine on the water company’s report, you must make sure that you use a combination of appropriate treatments to remove all traces of it.

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The problem of pure water in fish ponds

Also remember that just as tap water isn’t necessarily suitable for fish in general or Koi in particular, neither is pure water. Use a purifier and you’ll then have to address this by adding the correct cocktail of minerals to keep your fish healthy. Take a look at the ingredients of the various all-purpose and Koi foods such as those from Bradshaws Direct and Pondkeeper, and also consider the Koi food and supplements from Absolute Koi and other specialist suppliers.

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Maintaining tapwater purifiers for fish ponds

It’s essential to replace cartridges in your purifier regularly because the materials become exhausted and ineffective after a certain period of time, depending on how polluted your water is to start with.

Ensure that you use the recommended flow rate through the purifier cartridges. If the flow’s too fast the purifier will not be able to remove all the toxins. And, as ever with Koi keeping, you need to consistently monitor your water quality. Obtain regular water company reports, test your tap water and the treated water using reliable test kits or a specialist lab. Don’t wait until your fish begin to suffer to think about what your water’s made up of.

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7 top tips for choosing and using a tapwater purifier for fishponds

  • Ask local Koi dealers (i.e. those who are on the same water supply as you) how they test and treat their water.
  • Get a drinking water report from your water company or council. Tell them you’re a fish keeper so they give you the right information.
  • Find a laboratory (ask your Koi dealer or look in the Yellow Pages) that can test water for fish toxins at the appropriate sensitivity levels.
  • Along with your reports, note your pond’s volume, fish stock and health problems before talking to manufacturers of purifiers.
  • Check that the water purifier can cope with the levels of contaminants in your water supply.
  • Establish the effective life of the cartridge in relation to the typical levels of contaminants in your tap water, and record the date of first use, and when to buy a replacement.
  • Establish the life of the cartridge in terms of water volume, and install a water meter to log the cumulative total through the purifier.

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Range of water treatments

There is a huge range of different water treatments for fishponds, as just a few are illustrated below:

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