Water Quality: The Key to Healthy Koi


Most pond owners come to have a passion not only for the aesthetic of their pond, but also for the aquatic life that inhabits it. At Fitz’s Fish Ponds our passion lies with Japanese Koi and over the past 10 years we have learned much about the optimal ways to keep Koi healthy and this heavily relies on maintaining an ideal environment for the koi.  The type of advice we provide varies depending on a number of factors such as number of fish inhabiting a pond and whether it is a formal pond or a natural pond. We also have our Retail Managers that maintain the tanks in our stores as well as our Fish Care Specialist that works out of our farm and maintains the many tanks in the greenhouses at our farm. We have two 20,000 gallon tanks, six 10,000 gallon tanks, four 4,000 gallon tanks and 18 1,500 gallon tanks all inhabited with koi imported from Japan. That is a lot of water to maintain- which is why we have a water testing system in place, and know the importance that water quality plays in connection with fish health.  Our experienced team believes that pond owners and koi keepers should also make the water quality of their pond one of their main priorities when caring for koi.

Water Quality

Our team interacts with ponds every day and our retail managers and Fish Care Specialist are extremely knowledgeable about fish care and specifically how water quality is the most important factor in keeping fish healthy. Green Brook Retail Manager, Ryan Cardillo, always tells customers that “Water quality should be any pond owner’s top priority. This is why we do water testing so frequently.” He says, “If the water quality isn’t up to par, then if a fish is sick and a specific treatment is needed, nothing will work if there are issues with the water. This is the environment the fish are living in, which is why having a good filtration system and a good aeration system is essential to maintaining water quality and keeping fish healthy.”

Importance of Filtration and Backwashing 

While most pond owners know the importance of filtration, what role does the filtration system play in actually keeping the fish healthy? Essentially, the filter is a collector, it cleans the pond while collecting the fish waste. This is why it is essential that the filter be maintained and back washed on a regular basis, especially if the pond is holding a high stock of fish. The more fish that are held in the pond, the more waste that is produced. If a filter is not backwashed often enough and too much waste is accumulating, then this is when koi health issues such as bacterial infections and ulcers, both which are related to too much anaerobic bacteria in the pond environment, begin to emerge. So how often should one back wash their filter? This depends on so many factors that it is difficult to put an exact number on it. Essentially, with a higher fish load a filter will need to be cleaned more frequently. 

In a natural pond that has a river rock or pebble bottom, there are many gaps and holes in which there can be pockets of stagnant water. Although this can provide a beautiful appearance in the pond, they can act as traps for fish waste. This is why bottom drains are often utilized as they suck down larger waste and help eliminate stagnant water as this can cause serious health issues for the fish. If too much waste builds up it can generate a thick muck at the bottom of the pond trapping pockets of methane and sulfur gas, eliminating oxygen from the water. Oftentimes when this happens not only will pond owners notice bacterial infections in their fish, but they also might be literally gasping for air. Issues like this with the water quality can cause a major loss and fish death in the pond. This is why a high quality aeration system is so important for your aquatic life. 

Importance of Aeration 

Aeration has a number of benefits for the pond and aquatic life that inhabits it. An aerator pumps oxygen through the air stone and creates surface tension while also stirring the water around keeping the particles moving. This process ensures that any of the waste in the pond makes its way to the filter and helps to avoid bacterial collection on the bottom of a pond. In addition, Mike Milazzo, also known as “Fish Mike”, Fitz’s Fish Ponds Fish Care Specialist, knows just how much the Koi love the flow of water. He explains that, “At the farm, I keep water flowing within the tanks at all times. In addition to the aeration systems in the tanks, I make sure there is a constant drip of fresh water going into the tanks.”  Mike recommends that pond owners have multiple aerators in their pond to keep fish at optimal health– the aerator provides the fish with oxygen and also eliminates stagnation and the problems that could occur with stagnant water. This is why we recommend doing period water testings to your pond water to avoid any potential health issues for your fish that could be due to water quality. 

Water Testing and Temperature

At our farm, Fish Mike tests the water every other day to keep a check on the water quality in all of the tanks. We use the API water testing kit which tests for Ammonia, Nitrite, KH, Salinity, Nitrate and pH in the water.  What is revealed through the water test will then give an indication of what might need to be done or added to the water. Ideal levels for Ammonia and Nitrite are zero. If either of those approach 0.50, this is when we start to become alarmed. In order to rectify a problem like this we would do a larger backwash and add salt. In regards to the salinity of a tank, we are looking for levels that are between 0.10 and 0.30.  In order to measure the salinity, a salt test meter should be used. It is also important to note that if salt levels are too high, it can kill plants in the pond, however low levels of salinity should not impact the plant life too much. 

The pH of well water, which is what runs in our tanks throughout the day, is generally around 8 and koi can live in water like this, however we like to keep our pH range 7.5- 7.7. Getting freshwater into the tanks also helps to balance out the Nitrite levels– therefore adding fresh water into your pond will bring down to Nitrite levels if other methods of getting it down are problematic.

According to Fitz’s Fish Ponds Colts Neck Retail Manager Tom Swinarsky, “It is extremely important for pond owners to do periodic water testing. There are water testing kits available for pond owners to purchase and complete at their own leisure, however some pond stores, like ours, will take a sample of the water a customer brings in, test it, and then we are able to provide advice based on the results.”

Pond owners should also be aware of whether or not their water is city water or well water. If city water is being used to fill a pond, a pond owner can either add an in-line detox dechlorinator, which is the popular first option. A second option would be to physically attach a chlorine filter to the hose. Without eliminating chlorine from the water, fish may begin to die. 

The temperature of the water also matters significantly for the koi. The most active time for koi is when the temperature is between 68-85 degrees. Cold water temperatures slow down their digestive system, therefore when the water reaches below 68 degrees, the koi keeper should limit the amount that the koi are fed and switch to cold weather food. This is why having a thermometer for your pond is an essential.

Using Salt to Care for Fish

Fish Mike has done much research on the use of Salt and how it is not only used to maintain water quality, but it also assists in fish care and acts as a treatment for sick fish. He says that in the greenhouses this has made a huge difference in how he approaches caring for a koi that is showing signs of stress. 

He says, “When you notice a fish showing signs of stress, which could be going into a certain part of the pond and showing lack of movement or perhaps the fish develops an ulcer, one option is raising the salt levels in the tank. You can raise the Salt Level to 0.60 to help the fish heal more quickly than it normally would. Salt assists in the healing of injuries, promotes the formation of slime coating, improves gill function, reduces the uptake of nitrite, and decreases osmotic stress.”

It is important to note that raising salt levels should be done as a temporary treatment, it would not be safe to keep the salt levels this high in the tank at all times. While salt is a huge help and works well for our tank systems, it is not a “cure all” and in many cases other treatments or medications are necessary depending on the disease. If you have a water garden filled with plants, you may have to have a separate quarantine tank set up to treat the fish with salt water. 

It is possible to quarantine a fish that is sick so that the issues don’t spread to others in the tank or in the pond, however koi don’t like to be isolated, so it needs to be a good balance and isolated for treatment only, then reintegrated back into the tank or pond with the others. 

Ultimately, at Fitz’s Fish Ponds we strive to educate our koi keepers and pond owners to ensure they get to enjoy their pond and fish to the best of their potential. By maintaining and keeping a regular backwashing cycle on the filtration system, ensuring the pond is limited with stagnant water due to an aeration system, adding freshwater and salt to to the pond as need and doing frequent water checks, pond owners should be able to avoid most health issues with their koi and watch them live long and healthy lives.

Need help with the water quality in your pond? Reach out to us today by calling 908-420-9908!