Frequently Asked Pond Fish Care Questions

Q. How many fish can I have in my pond?

Be careful not to get carried away and overstock your pond. Fish need room to swim and grow.

Rule of Thumb: To account for all kinds of fish, keep your fish load under one-inch of fish length (excluding the tail fins) for every one square foot of water surface – about one goldfish per three to four feet of water surface area. Because Koi grow larger, place one Koi for every 10 square feet of surface area. Typically, Koi should be in ponds that are at least 1,000 gallons.

Avoid Overstocking the Pond
To maintain healthy fish and clear water, do not overload the ecosystem with too many fish. For a new pond, a good rule of thumb is one inch of fish per square foot of surface area. Once the pond is built, pond owners can add a few fish at a time over a 30-day period, allowing time for the pond and filter to be biologically ready to support the additional aquatic life. A mature pond can support two to three inches of fish per square foot. If your fish population exceeds these guidelines, you may need to increase the size of your filter.

Q. How do I add fish to my pond?
Selecting the fish: Be sure the fish dealer has brought the new fish into the store using sound quarantine procedures. You want to avoid adding diseased fish into your pond where they could infect the other fish. Avoid purchasing fish that are listless, pale in color, gasping or have fins folded back. If the tank contains several dead fish, purchase your fish elsewhere. A healthy fish is active and bright and has outstretched fins. If you are uncertain about the health of a fish that you plan to introduce into your pond, you may want to keep these fish quarantined in a tub of pond water and treat with TetraPond® Pond Fish Treatment. If after a week of observation, your fish shows no signs of illness, you may add the fish to the pond.

Preparing your pond for fish: Be sure that the water in your pond has been treated for chlorine and chloramines using a product such as TetraPond® AquaSafe®. If it is a new pond, make sure the pond and filter have been running for at least two weeks to allow the beneficial bacteria to colonize.

Taking your fish home: Typically you will buy a pond fish in a plastic bag of water from your fish dealer. Minimize the amount of time from the store to your pond.

Placing fish in the pond: Place the bag in the water for at least 30 minutes so that the water in the bag gradually matches the temperature of the pond. Open the bag to allow pond water to mix with the water in the bag for a few minutes. Gently pour the fish into their new home.

Q. What type of fish should I put in my pond?
Goldfish: These larger hardy goldfish do relatively well in poorer water conditions. They are known as good swimmers. Purchase fish that are at least two to three inches long; some can grow up to 10 to 12 inches long. There are many varieties of “goldfish” to choose from:
  • Comets, one of the most popular types of goldfish, have long slender bodies and are typically solid orange and metallic in appearance.
  • Shubunkin have longer, thinner bodies and are typically shaped like the common goldfish. There are two types: one has a long tail fin with broad, rounded fin lobes; the other has a short tail fin. They are primarily bred for their beautiful colors.
  • Fantails have shorter and rounder bodies and are distinguished by their “split” caudal fin, or tail, which is typically longer than the common goldfish’s tail.
Koi: Koi, or Cyprinus carpio, are ornate cousins of the carp family and can be easily identified by their whiskers. Their vivid coloration, striking patterns, longevity and impressive size make them popular pets. Standard Koi colors are black, white, yellow, orange, blue or red.
  • Taisho Sanke: Pure white Koi with distinct red and black markings.
  • Ohgon or neon Koi: Usually yellow, orange or gold metallic.
  • Butterfly Koi: Distinguished by their long butterfly fins.
  • Metallic Koi: Arguably the most eye-catching, their reflective silver or gold pinecone patterned scales give the pond luster.

Q. Should I change the fish diet during the year?
Yes, especially if you live in an area where the water temperature will dip below 50oF during the winter.

Change the diet based on water temperature:
  • In the fall when water temperatures fall below 50o F, switch your fish food to a quality wheat germ-based food, such as TetraPond® Spring & Fall Diet.
  • When temperatures fall below 39o F, stop feeding fish entirely.
  • In the spring, when water temperatures are consistently above 39o F, resume feeding wheatgerm-based foods.
  • When temperatures are above 50o F, you may feed your fish any of the TetraPond food diets. Use the TetraPond feeding thermometer to help guide you with food selection.

TetraPond® Spring & Fall Diet transitions fish in and out of cold temperatures. Compared with an animal protein-based food, a wheat germ food like Pond Spring & Fall Diet will spend 25% less time in the intestine. Good quality wheat germ products are formed from easily digestible plant ingredients, enhancing digestion and reducing the time it takes for the nutrients to be absorbed.

Why you should not feed when temperatures are below 39o F? Fish should only be fed when they are active and looking for food. No food should be offered if the fish are motionless near the bottom of your pond. When water temperatures are below 39o F, they will not be actively seeking food. Feeding fish below 39o F can lead to metabolic disorders. During the winter, fish will “hibernate.” Their digestive systems virtually stop, so food does not digest and can actually kill the fish.

Q. What should I do with my fish in the winter?
In most parts of the U.S., it is fine to keep your fish in your pond, providing the depth of the pond is deep enough so that the water does not freeze to the bottom. Unless you live in an area where your pond will be exposed to extreme cold, 18 inches depth is sufficient. In extremely cold areas, be sure your pond has areas 24 inches or more of depth.

Koi, Shubunkins and most goldfish survive winter by remaining inactive. Do not feed your fish when water temperatures are below 39o F. (See Fish Care questions about changing the diet during colder months.)

Use a pond de-icer to keep an area of the pond ice-free to allow for toxic gases to escape the pond.

Some fish, such as fancy goldfish, should be brought indoors during the winter. Check with your local fish dealer for advice on your specific fish.

Q. How much and how often should I feed my fish?
Fish should be fed one to three times a day during the feeding months, when water temperatures are 39o F and above. Rule of thumb: Feed only the amount your fish can consume within five minutes.

Q. How can I keep my fish healthy?
Maintaining fish in good condition should be the aim of every pond keeper. Pond fish are sensitive to a variety of factors, such as water quality and nutrition, that can weaken immune systems and make them susceptible to disease.

Water quality: Particularly important to water quality, and consequently fish health, are raised pollutant levels (i.e. ammonia, nitrite and nitrate) and sudden changes (or unsuitable values) of water pH and hardness.

Ammonia and nitrate levels: Excessive ammonia can have adverse effects on the fish. In most cases, fish will show severe signs of irritation and occasionally reddening on the skin and fins. Raised nitrite levels can be directly toxic to the fish. It leads to irritation of the gill and skin membranes and a reduced ability of blood to transport oxygen. At lower concentrations, fish immunity will be weakened, allowing parasite numbers to increase. Nitrates are unlikely to be directly toxic to pond fish, unless the concentration is greater than 50mg/liter. At lower levels, fish are weakened and prone to disease, poor coloration and poor growth. 

All fish are diseased: It’s important to understand that all fish are diseased. They’re all infected by at least one, and often several, species of parasites. These parasites are a natural part of the environment of the fish.

Q. How can I maintain a good pH balance?
Within sensible limits, the water’s pH is not critical for Koi; they happily survive in pH values ranging from 6.5 to 8.5. In a pond containing dense algae or plant growth, pH changes considerably in a 24-hour period. Plants and algae consume the bicarbonates that buffer the pH. At nighttime they respire, producing carbon dioxide which causes the pH to drop. During the day, they photosynthesize (use carbon dioxide and water to produce carbohydrates and oxygen), using up any carbon dioxide and allowing the water to return to its natural pH. Therefore the pH at dawn is likely to be considerably lower than at dusk. Because this change occurs slowly, it does not harm the fish. Use a TetraPond Pond Test Kit to quickly and easily monitor your pond’s pH level.

If the pH is outside the acceptable levels, altering the water quality may be necessary. Whenever possible, find the cause and remove it rather than trying to alter the quality of the water itself. A sudden rise or a high pH often results from the water coming into contact with untreated cement or limestone that is either present in the pond or surrounding area. The solution? Use a sealant on any cement in the pond and take precautions to drain water away from the pond. Conversely, a drop in pH may be caused by a buildup of organic debris, garden runoff, heavy rainfall or perhaps a malfunctioning filter.

Q. How do I know if my fish is ill and how do I diagnose the problem?
The following are symptoms of fish illness:
  • Gasping
  • Rubbing
  • Becoming darker or lighter in color
  • Appearing emaciated
  • Exhibiting listless behavior

Tips on diagnosing fish illness:
Prompt treatment requires quick and correct identification of the problem. Pay special attention to the time of disease onset and how quickly it spreads throughout the pond. See Tetra's fish illness guide here. Pond Fish can be afflicted with similar illness and deseases as Aquarium fish. This guide can help you spot them.

Use these guidelines to find the cause:
  • If one or two fish are affected and the symptoms do not spread to any other fish, then the cause may be a noninfectious disease or malformation.
  • If a small number of fish are affected initially, but the number gradually increases, then the cause may be an infectious disease.
  • If all fish are affected (or all fish of the same species/size) and the illness has spread very quickly, then the cause may be poor water quality.
  • Examine fish for signs of parasites. Place the affected fish in a large clear plastic bag so they can be easily viewed from all sides.

Q. How do I treat for fish illnesses?
Immediately remove and quarantine badly diseased fish to prevent the spread of disease. When two or three fish are affected or the disease is infectious:
  • Change 25 to 30 percent of the water and remove any excess debris. Use a water treatment that neutralizes the heavy metals, chlorine and chloramines from tap water, so fish will not be harmed.?
  • Treat the entire pond with a remedy that destroys harmful bacteria, parasites and fungus. 

Q. Why are my fish disappearing?
This is usually due to predators. The most common predators include herons, raccoons and ducks. If you suspect a problem, you may want to consider investing in a motion detector sprinkler. Note: These devices are not selective and work on people and pets as well.

Q. Do my fish need hiding places?
Yes – a fish’s natural behavior is to avoid open spaces because it is vulnerable and tends to get eaten when out in the open. Predatory birds can empty a pond. Aquatic plants like water lilies and iris roots offer shelter. Large clay pots placed on their side or black plastic crates can also serve this purpose

Q. How should I deal with pests like raccoons, herons or ducks?
If you suspect a problem, you may want to consider investing in a motion detector sprinkler. Note: These devices are not selective and work on people and pets as well.

Q. How do I tell a male from a female goldfish/Koi?
It is virtually impossible to determine the sex of a goldfish. The usual way is to wait until spawning behavior starts, usually in algae-laden ponds in the spring when days grow longer and the water temperature rises. The female will appear plumper and the males will chase the females, butting them to induce the release of eggs.

Q. Why is one fish chasing another one?
Spawning behavior can look like one fish is chasing another. You’ll usually observe this behavior in algae-laden ponds in the spring when days grow longer and water temperature rises. The female will appear plumper, and the males will chase the females, butting them to induce the release of eggs.