Koi fish are wonderfully colorful freshwater fish, which bring so much enjoyment to their owners. Koi keepers are responsible for the well-being of their fish. There are many complex elements to a pond and fish care. We have significant experience with caring for fish and ponds. But we continue to learn and develop more knowledge. We know a lot about fish but are very reluctant to call ourselves experts because so many so-called experts out there give bad advice. As a koi/pond fish keeper, you must provide your fish with a safe stress-free relatively stable water environment, quality nutrition, and reduce/prevent exposure to parasites/diseases.
Here are some of the most common problems we have seen over the years, which can cause problems, with some of our advice on how to prevent/reduce potentially costly mistakes for your fish in your pond. These are just our thoughts, there are always exceptions, please just use this information as a rough guideline when considering your specific pond issues as they arise.
Feeding Too Much!!!! - Throwing a handful of koi pellets into a pond and watching the fish feed at the surface, often in a frenzy of mouths, colorful tails, and much splashing, is a real delight, it is very easy (we have all done it) to get carried away and overfeed our fish. Do not overfeed your fish. As waste food and increased fish waste, have a negative effect on pond water quality, which often leads to serious health problems for your fish. To determine the correct amount of food your fish need, start with a set amount (appropriate for your pond setup, size, number of fish, and their size), all the food should be eaten within five minutes, if not reduce the amount you feed until all the food is eaten within five minutes.
Pond Water is Green!!!! - You have gone to all the effort and expense of creating your own little piece of heaven in your yard for you, your family, and your fish, but the water in the pond is green and cannot see your fish. They cause algae, which occurs naturally during the warmer months of the year. The use of a UV light unit, of the right size for your pond volume, typically built into the filtration system of a pond is a very reliable and quick way to eliminate green pond water. There are also chemical water treatments to temporarily reduce algae problems. An alternative method we have seen work well in a few ponds is to incorporate aquatic plants into the filtration system or a header pool above the main fish pond, the plants absorb the nutrients in the water algae need, preventing them from developing.
Have a UV unit but the water has started turning green again!!!! - the UV units you spent a small fortune on six months, a year ago are on but the water in the pond has started turning green once again. This signals that it is time to replace the UV bulb, because as UV bulbs age through use the of UV light they omit changes in frequency, from one that breaks down single-cellular algae to one that does not. The bulb is on, and you cannot see any apparent difference, but it is time to change that bulb. As you are doing that go ahead and replace the rubber O rings, they are relatively inexpensive compared with the cost of replacing the whole UV unit should water seep in and short out the bulb and electrics.
Avoid buying fish from everywhere!!! - Arguably the biggest risk to koi (and other pond fishes), are new fish introduced into an existing population of fish from a different environment. As that fish(s) may be a carrier of a disease that can have disastrous consequences, in some cases 80-100% of the fish in the pond are killed. To reduce the risk, always buy fish from a source with integrity. Always quarantine new fish before introducing the fish into your main pond. The quarantine system needs to be separate from the main pond, using different nets and taking every step possible to prevent the transfer of water from the quarantine system to the main pond. After a reasonable amount of time introduce one or two fish (your least favorite, as you are risking these fish) from your main pond to the quarantine system and monitor to see if there are any negative health effects on these existing fish. How long do you quarantine? Good question, ideally if practically possible, we would say at least a few weeks, preferably 4-12 weeks. Try to plan your fish buying. We know this is almost impossible because everybody gets tempted at koi shows and the pet store, too many impulse fish buys. Just have a reasonable quarantine system set up and ready to use. Avoid putting new fish directly into a pond with an existing fish population! Otherwise, there may be tears.