Koi Pond & Waterfall: Top 21 Most Asked Questions Answered


Q  What is the ideal depth for a koi pond?

A  In my experience of over 25 years, 4 to 5 feet is ideal. You need a minimum of 3 feet for koi fish for several reasons. Safety for fish from wading cranes they can not wade in 3 feet of water. Plus the water temperature in shallow ponds fluctuates too much with the changes in ambient temperature. The greater the volume of water, the longer it takes for the temperature to change. Warm water or fluctuating temperatures are unhealthy for fish.

Q  What is the ideal size for a pond?

A  The ideal size would be determined by the size of your yard. Its size should be proportional to the size of the yard. Also, the larger the pond, the greater the maintenance.

Q  What is your opinion on using a liner to construct a pond rather than using a hard molded or concrete one.

A  My recommendation is and always has been to use concrete. However, if you are on a tight budget or do not plan on living there for an extended period time, a liner would be recommended. In this case, you would have to add a thin layer of mortar between the liner and soil to prevent tree roots, ground squirrels, rats, mice, gophers or chipmunks from compromising the liner. The hard molded, preformed plastic ponds become brittle from the sun’s UV rays in just a couple of years. No good!

Q  What type of pond filter do you recommend?

A  That cannot be answered simply because many factors are involved. Do you have an existing pond with a submersible pump or above-ground pump? What’s the volume of the pond? Do you have fish, and if so, how many? What size plumbing pipe is being used? This is so involved, I have devoted an entire chapter in my construction manual to the subject. I have an 8000 gallon pond with above-ground pump and I use a pressurized biological bead filter. It takes 2 minutes to back flush with the turn of a handle and keeps my pond crystal clear.

Q  I have tons of algae hanging from the rocks in my falls and growing in clumps in my hand. What can I do to get rid of it?

A  When the first Polynesians settled in Hawaii between 300 and 600 AD, they were probably very annoyed by the aggressive, wild, pervasive taro plant, just like you are your algae. They tried to chop it down, burn it, stomp it, but to no avail. It just came back, so they eat it, and still do to this day. In fact, it’s a staple like peanut butter is to some Americans. Just kidding! However, if you told me it was watercress I would suggest eating it. Many pond stores will try to sell you a very expensive algaecide to solve your problem, but all you need to do is increase the salt content of your water. Some experts recommend one pound of rock salt to every 100 gallons of water. This will not hurt your fish; in fact, it will help to produce a healthy shine coat. However, it will harm most of your plants if you apply that dose all at once. Plus the dead and decaying algae will deplete the oxygen and this will harm your fish. Apply it slowly over a week or two, and be patient. It takes longer to kill it this way, but your fish will appreciate it! This topic is also a chapter in my construction manual.

Q  Should I keep salt in my pond on a regular basis?

A  If you maintain a specific gravity of 1.000, your fish will be less susceptible to ulcer and fin rot. And you will keep the algae from getting out of control.

Q  I am considering building a waterfall between my house and my neighbor’s against the fence. Will the sound of the falls annoy them if I let it run 24 hours a day?

A  The sound generated by a waterfall is called white noise, which is very relaxing and soothing, not annoying. I have several hundred clients who leave their falls running 24/7 and none have ever had a neighbor complain. In fact, they all appreciate the fact that they did not have to spend the money to enjoy the sound.

Q  How many koi fish can I put in my pond?

A  The amount could range from 150 to 250 gallons per fish. If you are starting out with small 6″ to 8″ long koi, they can reach 2 feet in three years, depending on how much food and how often you feed them. They could even grow to over 3 feet long! The overcrowding of fish produces stress and a lot of waste material. It can reduce the health of the fish and result in various diseases. Also, a less crowded pond is more pleasant to look at.

Q  Do I really need a filter in my pond?

A  Not in every case. If your pond is small and you have any guppies or mosquito fish and adequate water plants covering 1/3 to ´ of your pond, your pond will clean itself by means of the nitrogen cycle. The biological aspects of pond chemistry is well covered in my waterfall and construction manual.

Q  How long do koi fish live?

A  The average life span of koi in Japan is 70 years. Some have been known to live to 100 or more, such as the legendary Hanako, alleged to have lived for over 200 years. Unlike the amazing results of the meticulous care the Japanese give their koi, American koi live a fraction of that time, usually due to neglect and lack of care or proper environment.

Q  How can I protect my koi against predators?

A  Unfortunately, most people that come to me are frustrated people who already have a pond or a rather poorly planned pond. If your pond is shallow, less than 3 feet, or has a shallow end, the raccoons, coyotes, cranes, egrets, etc. have easy access to your fish. You may think your fish are safe because you have a deep end for the fish to retreat to. Well, you and your fish are dead wrong. A crane will stand perfectly still for 10 to 20 minutes waiting for the koi to forget he is there. Some will regurgitate chum into the deep pond, luring the fish to the surface. Your only solution is a net, or try the crane statue, scarecrow, or high-frequency sound emitters for smaller animals. However, one of my clients watched a crane land next to his crane statue. While the scarecrow was pelting him with a stream of water, it snatched up one of their prize koi.

A critter-proof pond is over 3 feet everywhere and has a raised deck 13″ minimum over the water surrounding the pond. Raccoons cannot swim and catch fish at the same time, and they or the birds will not be able to reach the water.

Q  I would like to have a koi pond but I live in Michigan and every year ponds and lakes freeze over. Will they survive?

A There are fish in those lakes you are talking about: blue gill, bass, sunfish, carp, and they all survive. And guess what? Koi are in the carp family. Koi were originally raised for food in Japan. They would grow rice in the summer and then flood the rice patties and raise koi in the winter, cutting holes in the ice to catch them for food. However, your pond must be 4 ´ to 6 feet deep to ensure the water stays about 40 o the bottom. Turn off the waterfall and bottom drain, draw water from the skimmer to keep the bottom still. Place swimming pool solar blankets over the surface. If your pond is deep enough, you can let it freeze over. However, you need to install a horse tank heater to keep a hole open in the ice to allow any ammonia gas from rotting debris on the bottom to escape. If your pond is less than 4 ´ feet deep, take the koi indoors for the winter and place them in a garage or basement tank.

Q  Can I keep koi and goldfish together?

A Yes, you can. They are both cold water fish and members of the carp family. Most other cold water fish can also swim together, such as shubunkins, rudd, orfe, blue gill, mosquito fish, guppies, sunfish, bass, etc. However, only in deeper ponds where the mean temperature is 65 degrees or less on the bottom for bass, sunfish and blue gill.

Q  Should my pond have a bottom drain?

A  First of all, a bottom drain is essential for a healthy pond. However, if it is exposed and the suction is strong enough, turtles or fish can get stuck to it and not be able to get loose. Therefore, two drains should be hooked in series to relieve the pressure between them, just as in a swimming pool. Bottom drains draw falling waste from the fish before it reaches the bottom, keeping it clean. Areas where it does build up can be swept to the drains for easy cleaning. If you are using a submersible pump or pulling the water from a skimmer, water is not circulating properly on the bottom of the pond. That is where rotting debris is producing ammonia and other toxic gases.

Q  My pond water is very clear, but my fish are dying. What is wrong?

A  Drinking water might taste good, smell good, and look clear. But some of the most toxic chemicals that are known to cause cancer are colorless, odorless and tasteless. I recommend that you purchase a test kit form a pond store and check your water regularly. Nitrates, nitrite and ammonia are all detrimental to fish. Ammonia and nitrite can, at high levels, be fatal to fish. These substances are dissolved in the water and consequently are impossible to detect by the clarity of the water and they can break down the fishes’ immune system.

Q  What type of filter do you recommend?

A  For any pond over 1000 gallons, I recommend a pressurized biological bead filter that can be back washed. I have used Aqua Ultraviolet Ultima II filters for years. Most larger pond suppliers carry them. Their filters range from 1000 gallons to 10,000 gallons. Up-flow and gravity flow filters require regular cleaning, which is a filthy job. The filter media is packed with stinky, putrid fish waste and decaying pond scum. As you handle the filter screens, media, scrubbers, etc., you will have little white feces-eating worms that are 1/16″ long crawling on your hands and arms. Not to mention the noxious smell that burns your eyes and lungs.

It cost pennies on the dollar to make, yet dealers charge a fortune. You pay the price for the filter and in the time it takes to maintain it you pay an additional cost for your time maintaining it. With a pressurized filter, it only takes the turn of a handle for 2 to 3 minutes and the filter is clean. The waste water is not wasted either. You can water your plants with it using the discharge hose. If you can imagine, that brown, colored, stinky water is packed with nitrogen. It’s better than Miracle Grow T.M. I have used my 6000 gallon Ultima II for over eight years and it works as well now as they day it was installed. Happy, happy fish!

Q  How much does an average pond cost?

A  What is average? It depends on whether you are talking about a liner pond or a professional concrete and rebar pond. A typical liner pond can be 6 feet by 8 feet, and depending on who is installing it, could cost between $2,500 and $3,500. The other dimensions are pretty much proportionate. Liner ponds are susceptible to leaks from punctures, gophers, and rats, etc. Concrete ponds last for decades and on the average cost only 20% more than liner ponds.

Q  My pond is green and I can not see my fish. What should I do?

A  Your challenge is algae (suspended planktonic algae), which does not directly hurt the fish. However, algae gives off oxygen during the day from photosynthesis. But unfortunately, it uses up oxygen at night. In addition, it is unsightly and blocks the view of the fish. You can increase the salt content or install an ultraviolet light, which not only kills spore algae but kills the bacteria that causes the water to become murky and stinky.

Q  I heard that UV light will also kill the beneficial bacteria. Is that true?

A  If I say “No,” I am calling many so-called professional experts liars. So I will put it this way. All the beneficial pond bacteria such as aerobic or anaerobic bacteria, nitrobacter, etc., reside in the filter or in the decaying debris at the bottom of the pond. They aren’t floating around in the pond. Bacteria and algae containing pathogenic disease are, and as they pass through the UV light, they are eradicated.

Q  Do I need a waterfall for my pond?

A  With no hesitation, YES! Most definitely. First of all, waterfalls are beautiful to look at. The sound is soothing and relaxing and the water moving over rocks generates negative ions which are added to the air. As you breathe negatively charged air, it relieves stress and anxiety. Waterfalls also add extra oxygen to the pond. Waterfalls are a must!

Q  I heard concrete ponds will leach alkali into the pond. Is that true?

A  Yes and no. A poorly constructed concrete pond will, but only until algae starts growing on the sides. Also if the pond is constructed of 3500 psi concrete and coated with Thoro-seal T.M., it is impossible for alkali to leach out. Plus, if you use Doug Hoover’s secret mortar mix formula, the mortar in the waterfall between the rock will not leach either.

Q  What is the advantage of building a waterfall using concrete and mortar?

A  A major reason is that the rock will be securely mortared in place, preventing a serious accident from rocks sliding, as with a liner waterfall. Trust me, some day, some adventurous child will climb onto it. That is a lawsuit in the making.

Happy koi, peace & joy.

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