Advice by Chris Neaves.

Don’t place rocks inside your pond. It may look good when you start a new pond but rocks will injure the Koi, take up space to reduce the water volume and debris will accumulate around/under them and most of the time contributes to the Total Oxygen Demand of the pond. Anaerobic situations will develop in the accumulated dirt.

Don't use plants to oxygenate your pond.  Water lilies will not oxygenate your pond. Water lilies are great snacks for Koi and Koi love to dig into the soil around them. This digging is not really beneficial to water clarity! Lilies are good for providing shelter against the sun and they remove a little bit of nitrates from the water. It is however a misconception that lilies can out-compete algae for nitrates in a pond and therefore prevents green water. It is mostly the other way around, the algae will survive. Lilies can add an aesthetic dimension to a pond if the resident Koi allows that. Plants that oxygenate pond water are mostly those that are totally submersed and during the photosynthesis stage will release oxygen into the pond through their leaves. Just remember that the reverse will take place during the night. Oxygen will be taken up by the plants and may lead to the demise of your Koi. Relying on plants to oxygenate the pond is therefore not sustainable. It is not advisable to place fertilizers in the pots containing lilies. Fertilizers may be harmful to your fish and will definitely stimulate algae growth in the pond.

Please don’t take advice freely given by a person who knows a friend that keeps Koi. The terrible scenes that I have encountered may give Stephen King some ideas when he writes a new book. I have encountered ponds where owners added Chlorine to the pond to get rid of algae, dose the pond with Dettol to “cure” ulcer disease and many more idiotic suggestions by friends. Remember there are weird people around.

Don’t over-medicate! Use the correct dosage. Even under-medicating has its own disadvantages, like stressing the fish without the desired results. Normally a follow-up mucus scrape and a check for parasites is the best way to go. Remember the water temperature and water hardness will have an influence on the effectiveness of the medication. It is always advisable to do a follow-up check a few days after the medication.

Please don’t run the pump on a timer or switch it off during the night. Remember that the Total Oxygen Demand (TOD) in a pond still exists whether you go to bed or not. Besides the fish, there are millions of organisms in a pond that rely on oxygen to survive. With no waterfall or venturi to keep the Dissolved Oxygen Content (DOC) high enough, you may wake up to witness a horror. Pumps must run 24/7 to ensure enough oxygen in the pond and also to prevent bacteria in the filter to become anaerobic and start to release toxic substances. During this time, the Koi also do not stop excreting waste products like ammonia etc. 

Don’t overfeed! Koi food is expensive and overfeeding will place a strain on the filter system and may result in water quality problems. Water quality that falls outside the acceptable parameters will encourage bacteria and parasites to take advantage of stressed fish to proliferate and cause serious problems. Feed one or two times a day as much as the Koi will eat in say five minutes. Remember Koi resembling a Sumo Wrestler is now out of favour. A Koi resembling a 100meter sprinter is more acceptable. There is a saying that a hungry Koi is a healthy Koi. Just don’t overdo the hungry bit! Don’t feed your Koi if your pump goes out for whatever reason. Koi will use more oxygen if they are fed.

Don’t place newly purchased Koi directly in your main pond. The dealer may have quarantined the fish, but the quarantine was in his system and the new fish should be introduced to your pond/water gradually to get used to new surroundings and possible pathogens. For many years there were debates whether to quarantine or not, but with the danger of virus infections and resistant strains of bacteria, it is now the norm that quarantine is a must.

Don’t change all the water in the pond at once unless absolutely necessary. “Mature” water is as much of an asset as a mature bio filter. Sudden temperature changes as well as pH changes may adversely affect your Koi.

Don’t put too many Koi in your pond. It is always tempting to add more Koi but remember your Koi will require more oxygen and more room as they grow larger.

Don’t keep the water level of your pond too close to the top edge of your pond. The Koi may jump out.  Allow at least 15 cm clearance.

Don’t use insecticide sprays, powders, or pellets near the pond.

Don’t just top the pond up when needed. All water available consists of some salts, metals and other impurities that got into streams through pollution etc. These end up in the pond. The fish waste is also converted into nitrates and proteins that also accumulate in the water. If the water level gets low through evaporation, it means pure water went into the atmosphere leaving all the impurities behind. Over time it will accumulate to unacceptable levels. The purpose of a water change is to dilute these accumulated impurities. It is therefore essential to take some water out and replace it with fresh water to dilute the accumulated impurities to the benefit of the Koi. It is also better to replace say 10% water at a time that to do ten small 1% water changes. You can do the calculations and rather leave it!

Don’t listen to those landscaping people that tell you a pond should be all natural and don’t need a biological filter. There is nothing natural about a concrete/plastic/fiberglass pond that is stocked ten times more than a natural water body and above all, have water that is re-circulated over and over.

Don’t assume that your Koi are happy and playful if they jump around the pond or play at the waterfall. More often than not, it is an indication of water quality problems or a parasite infestation!