Do your Koi look lifeless or have scales missing? This could be a sign that they are stressed and possibly suffering ill health. Losing a pet Koi is very distressing. The cause could be poor husbandry and often a result of deteriorating pond water quality. A lack of oxygen could also be the cause.

Water quality is a key factor to the health of fish who become increasingly stressed in poor conditions. There are a number of factors that can affect pond health such as local climate, size of pond, number of fish stocked, number of aquatic plants and the type of filtration system installed.

Koi are cold water fish and so do best in ponds that are in partial to full shade (geography dependent but best to avoid Koi pond water getting too warm). They can survive all but the coldest winters when ponds freeze over. Koi require more maintenance than goldfish and do more damage to pond plants nibbling on them only.

How to maintain healthy conditions for koi

• avoid spraying insecticides or pesticides on to flower beds that are close to your pond and put measures in place to prevent rainwater run-off (unless your garden and pond are on flat ground!). Use natural methods of pest control to reduce chemicals entering your pond and affecting the water quality.
• test the pH of your pond water fairly regularly. Fish thrive in water which has a pH of around 7 to 7.4. High ammonia and nitrate levels are an indication that there are too many fish in your pond or the filter system isn’t coping. The role of a filter system is to clean the pond water and keep it free of bad bacteria.
• carry out a partial water change weekly.  This helps to remove pollutants from the water. The advice on how much water is exchanged varies amongst pond experts. Start by doing a 10% change and monitor the water quality between changes. If 10% is not enough to remove pollutants then increase the volume. No more than 50% should be changed to avoid stressing the natural ecosystem and fish. Use a pump, pond vacuum or hose to remove water from your pond. Replace with harvested rainwater or dechlorinated tap water.
• a garden pond is a closed water system where water leaves only via evaporation leaving behind pollutants. Ponds need to be installed with a good filtration system to remove fish waste – which if not removed release ammonia into the water. Bacteria in the water converts ammonia into nitrates which is then processed by plants and algae.
• reduce levels of algae by growing aquatic plants which cover 50 to 70% of the water surface. Plants will also offer a protective habitat to fish. They also absorb nutrients in the water reducing algae growth
• remove organic mater from your pond water before it sinks to the bottom and starts to decompose – and becoming a food source for the growth of algae.
• the greater the surface area of a pond the greater the amount of oxygen so always build a pond as big as your garden space will allow.

Koi can thrive outdoors for many years in well nurtured and maintained garden ponds. A raised, vertically sided pond lined with a rubber Epalyn or Butyl pond liner is more of a deterrent to pond predators than a pond on ground level. There are, however pond guards and protective aids available for all pond types and shapes to discourage predators visiting and reducing your goldfish numbers.

Koi are friendly and add so much character to a garden pond. They are hardy provided you follow the advice shared in this article. If you can add anymore advice, we would love to hear from you.