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I started off with 4-inch koi and now they’re 8 inches. How big will they get before they stop growing? | Decorative Ponds & Water Gardens Q & A

Q: I started off with 4-inch koi and now they’re 8 inches. How big will they get before they stop growing?

Q: I started off with 4-inch koi and now they’re 8 inches. How big will they get before they stop growing?

Lauren – Lincoln, NE

A:  In an ideal environment—a supersize space with pristine water conditions at a stable 75 degrees Fahrenheit—an adult koi can reach a whopping 3 feet long. A yard! Nearly a full meter! Yep, that’s a really big fish.

Don’t worry: Chances are slim that your finned pal will grow to that immense length, but you can help it reach its full potential. Koi will keep growing and growing throughout their lives, sometimes faster than others. How fast and large they grow depend on several factors, including:

  • Water quality. Clean water pumped full of oxygen will promote a fish’s health and growth, while poor water quality can stunt its growth. Koi will tolerate a dirty, cloudy environment, but their development and vitality will suffer. Make sure you have an aeration kit in place and are using beneficial bacteria from the DefensePAC® to keep the water crystal clear.
  • Water temperature. A steady 75° F will keep koi in a more active growth state where they’re building muscle and body mass like crazy. Cooler or fluctuating water temperatures trigger a slower growth rate as they slow down their metabolism and activity level. If you live anywhere other than in the tropics, expect to see slower growth in the winter months.
  • Nutrition. Food—and how much of it they eat—matters. Fish food that’s packed with protein and vitamins is formulated to help koi grow and develop. Some also contain ingredients that boost your fish’s vibrant colors.
  • Genetics. Genes play a huge role in how large a koi could grow in the right conditions. Colossal parents often produce colossal offspring, and if those fry live in a spacious pond with clean, aerated water and good food, who knows how big they’ll get!
  • Age. Like most living things, koi develop faster when they’re young and slower as they age. Your 4-inch koi quickly doubled in size because they’re still adolescents; as they get older, their growth rate will slow down.

If you have big plans for your koi, give them an ideal ecosystem and good grub. Your colorful friends may not reach that 3- or 4-foot mark—but you never know!

Pond Talk: What’s the largest koi you’ve ever had—or seen in person?

Energy Efficient Design For 24-7 Use - The Pond Guy® Water Garden Aeration Kit

Is it better to rake out as much of the weeds and algae as I can before treating? | Ponds & Lakes Q&A

Q: Is it better to rake out as much of the weeds and algae as I can before treating?

Q: Is it better to rake out as much of the weeds and algae as I can before treating?

Sherry – Casselton, ND

A: It makes sense to want to remove as much of the plant nuisance as possible before spraying them with algaecides and herbicides. But, in general, it’s better to treat and kill the unwanted growth first – and then rake out the dead debris. Why? Let’s take a look at how weed and algae destroying chemicals work.

Contact Chemicals

A contact chemical, like Algae Defense®, needs to make contact with algae in order to kill it. If the chara, filamentous algae or planktonic algae are cut or broken into smaller pieces, it’s harder for the chemicals to make contact. Because algae grows by fragmentation rather than a defined root system, it’ll just keep on growing. So it’s better to leave the algae as-is before treating.

Systemic Chemicals

A systemic chemical, like Shoreline Defense®, works by being absorbed into the growth system of emergent shoreline weeds, like cattails, via their leaves and roots. As it does so, it kills the plants. Cutting the plants down stops the absorption process and prevents the chemical from getting into their system. As with contact chemicals, treat first.

Treat, Then Rake

After you’ve treated and killed the problem plants, then you should pull the dead debris from the pond with a weed cutter and rake. That will prevent all that decaying matter from becoming fertilizer for future algae blooms.

If you miss some of it, your aeration system and natural bacteria can do the work for you. An Airmax® Aeration system keeps the water oxygenated and moving, while the beneficial microorganisms in our natural bacteria products break down the debris.

Pond Talk: How have your algae blooms been this year? Better, worse or the same as last year?

Skim Dead Algae & Vegetation - The Pond Guy® Pond & Beach Rake

How do I calculate what size basin I need for a pondless waterfall? | Decorative Ponds & Water Gardens Q & A

Q: How do I calculate what size basin I need for a pondless waterfall?

Q: How do I calculate what size basin I need for a pondless waterfall?

Robert – Waverly, TN

A:  With the help of a few friends, installing a pondless waterfall is an easy way to upgrade your land- or waterscape. If you are planning to design and build your own feature, here’s how to do the math to determine your basin size.


Step 1: Calculate total amount of water in your stream

Sound tricky? It’s not. To calculate the water that’s in motion in your stream, first measure your stream’s length, width and depth. Then plug those numbers into this equation: L x W x (0.25 x D of stream, generally 1 to 2 inches) x 7.48.

Here’s an example. If your stream is 25 feet long, 2 feet wide and 1 inch deep, the equation would look like this: 25 x 2 x (0.25 x 1) x 7.48 = 93.5 gallons.

Step 2: Calculate amount of water your basin needs to hold

As a general rule, you will need your basin to hold 2½ times the amount of water in your stream. To find out how much water your basin will need to hold, multiply the gallons of water in your stream by 2.5. In the above example, it would be 93.5 x 2.5 = 233.75 – so your basin would need to hold 233.75 gallons of water.

Step 3: Determine the size basin needed to hold the water

Here’s where things get a little tricky. You’ll likely use boulders, stones and other décor in your design. Well all that rockwork will take up space for water, and so you’ll need to go with a larger vessel.

Try this quick equation that will help you determine what size basin you’ll need with boulders: L x W x D x 2.2 = gallons of water the basin will need to hold. To give you an idea, a 5 foot by 10 foot basin that’s 3 feet deep and contains stone will hold 330 gallons of water.

A space- and cost-saving option is to use a basin matrix in place of some of the boulders. A basin matrix is a strong, 27-by-16-by-17½-inch hollow box that’s perforated with half-inch holes to allow water to collect and pass through. You can stack them together and landscape right over them. Each basin matrix holds 31.5 gallons, adding valuable water volume without increasing the size of the basin. Don’t forget to add a pump vault for easy access to your pump.

Go with a Kit

If you aren’t trying to customize a large waterfall, consider investing in a pond free waterfall kit, like PondBuilder™ Cascading Falls Pondless Kits. They contain all components you’ll need – from underlayment and liner to a waterfall box, pump, basin matrix and plumbing – with predetermined dimensions to help you create your water feature.

Pond Talk: What’s the largest size boulder you’ve installed in your water- or landscape?

Create A Low Maintenance Waterfall - PondBuilder™ Cascading Falls Pondless Kits

What can I do to help out a fish that was attacked by a heron? | Decorative Ponds & Water Gardens Q & A

Q: What can I do to help out a fish that was attacked by a heron?

Q: What can I do to help out a fish that was attacked by a heron?

Lori – Glen Forney, PA

A:  Ouch. A heron attack isn’t pretty – and it’s potentially deadly to your fish. Unfortunately, you can’t call 9-1-1 or an emergency fish veterinarian for a pond call, but you can try some things that could save your pet’s life.


  1. Examine, Triage: The first thing to do is examine the victim and do some triage. Capture the injured fish in a pond net and take a closer look at its wounds without removing it from the water. How severe is the injury? Are there just a few scrapes, or does the fish have an open wound?
  2. Minimal Injuries: If your fish’s injuries aren’t too severe and it appears to be normal except for a few scrapes, leave it in the pond and add some Stress Reducer PLUS to the water. The liquid formula will help to calm the fish and rebuild its slime coat, which defends it against infection. You might also want to add some soothing salt to the water (read about it here).
  3. Remove and Isolate: If your fish is severely injured, set up a quarantine tank with pond water and an aerator, add some Stress Reducer PLUS, put it in a shaded and protected area, and gently move the fish from the pond to the tank.
  4. Watch for Infection: Keep an eye on your fish while it’s in the quarantine tank. Because damaged tissue becomes a breeding ground for bacterial and fungal pathogens, watch for signs of infection. If you see split or ragged fins, slimy patches or red ulcers on its body, or any other unusual symptoms, use CrystalClear® Wipeout™ or API® MelaFix to heal the wounds and restore damaged tissue.

While your finned friend is recovering, makes some plans for how you’ll guard your pond against future attacks. A Blue Heron Decoy will dissuade the real things from stopping by for a snack. Pond netting will prevent birds from reaching the water. Floating, submerged and marginal aquatic plants give your fish somewhere to hide, as do fish shelters, like the Koi Kastle. Set your fish up for safety – especially since that heron will be back for seconds!

Pond Talk: Have you ever nursed a sick fish back to health?

Reduce Stress & Heal Damages Tissue - Pond Logic® Stress Reducer PLUS

I would love to have ducks at my pond. Is there any harm, and how do I attract them? | Ponds & Lakes Q&A

Q: I would love to have ducks at my pond. Is there any harm, and how do I attract them?

Q: I would love to have ducks at my pond. Is there any harm, and how do I attract them?

Jerry – Cass City, MI

A: Ducks certainly make an entertaining and colorful addition to a pond or lake. Various species of these plumed wetland visitors grace just about every continent and climate on planet earth – including sub-Antarctic islands like South Georgia and the Aucklands to oceanic locales like Hawaii and New Zealand.

Despite their worldwide distribution, getting ducks to call your pond home can be a challenge. But you can attract them if you understand their specific needs.

Pondside Open House

The duck types that frequent ponds include mallards and wood ducks, along with Muscovy ducks, black-bellied and whistling ducks. Ducks are omnivores and like to eat a wide range of foods, from small fish, eggs, snails, worms and bugs to grass, weeds, seeds and berries. In general, they require a lot of space and copious amounts of water in the form of marshes, lakes or large ponds. Aquatic plants, like reeds and water lilies, make them feel at home, as does concealed areas with tall marsh grass and shrubby cover for nesting and hiding.

Attracting the Flock

Providing a duck friendly habit is the best way to convince the feathered visitors to stop by, but here are some expert tricks to make your pond more appealing:

  • Create a Mess Hall: Set up feeding areas by clearing out an area or providing large, low platforms, and toss out some cracked corn, spilled birdseed and kitchen scraps. Don’t feed them by hand, but use goodies to pique their interest.
  • Plant a Duck Garden: Berry bushes can help draw ducks. And if you have a garden area near your pond, use mulch to attract tasty insects and earthworms.
  • Offer a Nest Box: Though ducks will nest in a variety of places, from ground nests in grassy areas near the pond to brush piles and hollow logs, provide them with nest boxes to help attract nesting ducks.
  • Install a Fountain: Ducks flock to the sound of splashing, so consider installing a fountain or waterfall in your pond.
  • Use Natural Décor: Add some half-submerged logs, overhanging shelves, marsh grasses and marginals, aquatic plants and brush piles to your landscape.
  • Add Some Decoys: A duck decoy pair floating quietly on your pond will attract the attention of the real-life things. They’ll swoop down to investigate and (hopefully!) decide to stay for a while.

Duck Dangers

Unlike a Great Blue Heron, ducks will leave your fish alone – but they can trigger other problems. If a lot of them are visiting, they can cause water quality issues (which can be remedied with the beneficial bacteria in Pond Logic® PondClear™). They could bring in unwanted weeds, like duckweed and water milfoil, that weren’t present before. The ducks, ducklings and eggs could also attract feral cats, raccoon, skunks and other predators.

Having these colorful beauties visit your pond, however, is worth the hassle. When they do stop by, observe them from a distance – and enjoy bird watching!

Pond Talk: Do ducks visit your pond regularly?

Help Attract Ducks To Your Pond - Flambeau® Storm Front™ Mallard Decoy Pair

I have an old sump pump. Can I use it to create a fountain for my pond? | Ponds & Lakes Q&A

Q: I have an old sump pump. Can I use it to create a fountain for my pond?

Q: I have an old sump pump. Can I use it to create a fountain for my pond?

Nick – Linwood, KS

A: Sounds like you want to do some “upcycling” and save a little money while making use of old equipment that’s sitting around. What a fun project, and something you can show off to your friends!

Yes, you can certainly transform that old sump pump into a fountain for your pond – but whether it works will depend on what you want to do with that fountain.

Sump Pump Fountain?

A sump pump is traditionally used to remove water that’s collected in a basement. It pumps the water away from the house to a place where it’s no longer problematic. It’s not really designed for long-term continuous use, and so using a sump pump to create a spraying fountain might decrease its life expectancy. Replacing it could be costly.

There are other factors to consider, too. A sump pump might cost more to operate. You’ll still need to create a way to anchor or suspend the motor and create a spray. And you’ll need to extend the power cord long enough to reach a power source safely – which will require trial and error or fancy engineering.

If you’re a build-it-yourselfer in search of a challenge and plan to not use it for long-term continuous use, go for it! If not, consider purchasing an actual fountain.

Out-of-the-Box Easy

For those who are looking for an easy, cost-effective and trouble-free way to add some splash to a pond, buying a pre-manufactured decorative fountain has its benefits, including:

  • They come with pumps that are designed to be used as a fountain, so they create much more water movement and a heavier spray that’s less affected by wind and pump-clogging floating debris.
  • They can be used as an aeration system in ponds less than 6 feet deep.
  • All the engineering work is done for you! After a quick installation, you’ll have a decorative spray and a power cord that’s long enough to reach the shore.
  • Some, like the AquaStream™ Fountain and Light Combo Kits, come with decorative options, like lights and different spray patterns.

Whichever you choose, it’s always a great idea to create movement and aerate the water. Your fish and plants will appreciate it, and you – and your guests – will, too!

Pond Talk: Have you ever made a decorative fountain with upcycled pieces and parts?

Enjoy the Sound of a Fountain - The Pond Guy® AquaStream™ 1/2 HP Fountain

2,000,000 Views & Counting – Thank You!

We have surpassed 2,000,000 views!

Thank you for making The Pond Guy Blog the most read blog on pond, lakes, water gardens and water features!

We have posted over 650 times on topics ranging from building ponds to fighting leeches to fish hiding to eliminating cattails. If we still have not answered your burning pond question, please feel free to comment here about what you want to learn more about.

Thank you for coming along for the ride. We do not plan on slowing down so we hope you continue to join us weekly to learn about different pond topics.


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