100, 150, 200 and 300 Gallon Small Koi Pond The Ultimate Guide

A small garden pond is a great way to keep some fish while keeping the cost low.

If you have a space shortage you can build one in your garden, balcony, and even in the room.

The most common small pond sizes are –

  • 100 gallon pond
  • 150 gallon pond
  • 200 gallon pond
  • 300 gallon pond

In this article, I will walk you through everything you need to know about a small pond for fish.

A small garden pond

3 Ways to Build a small gallon Pond

Using Pond Liner

Pond liner is widely used to build medium and large garden ponds. It is a rear practice to build a 100-gallon pond with a pond liner. Because such small size ponds are built with preformed pond liner or stock tank.

But that doesn’t mean you can’t build a small pond with a pond liner. It is still possible to build such a small pond with a liner if you want. You will need a smaller size pond liner for this purpose. You can find good pond liners at amazon and eBay for 100 gallons, 150 gallon, 200, and 300 gallon ponds.

Using Preformed Pond Liner

Preformed pond liners are widely used for building a small outdoor fish pond. It takes very small effort and time to build a pond with this.

Preformed pond liners are easily available. Normally the volume ranges from 30 gallons to 600 gallons. So, if you want to build a 200 gallons pond with this, it is still possible.

To build a pond with a preformed pond liner, you need to dig the soil according to the size and shape of the liner and place the liner in that.

In Container or Stock Tank

If you want to build a small gallon indoor pond, the best way will be using a container or stock tank. It is also popular for balcony ponds. Stock tanks are made of galvanized steel, plastic, or Rubbermaid. Stock tanks are available from 50 gallons to 600 gallons size.

Making a pond with a stock tank or container is super easy. It will take you roughly 2 hours. Just place it in your preferred place, install the pump and aerator, add some plants, and you are ready to stock the fish.


Adding Plants

A pond without plants is always incomplete. They increase the beauty of the pond and helps to keep the water clean. Plants also make a good hiding place for fish. Some fish also spawn in the roots of the plants.

You have to be careful while selecting plants for your small pond. Don’t add large plants as they will take up the place.

If it is an outdoor pond, you need to add some of the plants to the shoreline. Also, add some floating plants to your pond. It will make the pond charming and help to keep the temperature low.

You can also add some submerged pond plants. they are good for oxygenating the water.

For preformed and stock tank pond you have to use mall plastic container for plants so that plant will not fully be submerged in water.

Some good plants for a small fish pond are –

  • Water lettuce
  • Creeping Jenny
  • Cardinal Flower
  • Hornwort
  • Sweet Flag
  • Water Hyacinth
  • Corkscrew
  • Anacharis


If your pond liner or tank bottom is visible, it looks odd. Rocks also help to culture beneficial bacteria and keep the water quality good.

Therefore, you have to add some rocks to the pond bottom. You can also build a pond retaining wall with rocks. Don’t use uniform size rocks, it looks bad. Rather use a mix of all-size rocks for your pond.

Fountain and Aerator

Having a fountain in your pond will take the beauty of it to the next level. It also helps to aerate the water. Aerating is important for a pond because it adds oxygen to the water and fish can’t live without oxygen.

You don’t have to get a big fountain for your small pond. Small fountains with a built-in pump available. Just make sure it can serve enough flow for the pond.


Having a spillway in a very small size pond is very rare because there won’t be enough water to maintain the minimum flow.

But you can still have a small spillway for your pond. I saw a guy install a small bamboo-made spillway in his stock tank pond. There is no need to buy a spillway, you can make one easily.

Lighting the Pond

Lighting your pond will increase its beauty. You can use a submersible or downlight for this purpose. Downlights are better than submersible lights as they last longer.

Normally, pond lights are LED lights. You can also use solar pond lights if you want. It will save you money in the long run.

For your indoor pond, you can install ceiling lights or clamp-on lamps, or LED grow lights. In indoor installing grow light is necessary because pond plants need it to thrive.

Choosing The Right Pond Filter

There are many types of pond filters available. The filter you need depends on the size of your pond.

For a small pond, you don’t need a mammoth filter. Two Spong filters are enough for filtering the water. They are easy to install and don’t cost much. You can power them with your pond pump.

Some people use bio-balls for filtering the water. They are good when you are super concerned about water quality.

If you notice too much algae in your pond, you can use a combo of filter and UV clarifier. This works really well for maintaining the water quality and killing the algae.

Choosing the Right  Pond Pump

It is recommended that you recirculate the pond water every 2 hours. Therefore, you will need 50 gallons per hour pump for your 100 gallons pond and 100 gallons per hour pump for a 200 gallons pond. For 150 gallons, the pump capacity should be in between these two.

But the pump size may increase due to various reasons. If you stock more fish than recommended, you will need more flow. Again if you have both spillway and fountain, the size of your pump will increase as well.

Pumps are available in two types, External and Submersible. I will advise you to use a good submersible pump. It will not create any hoise as it is kept underwater. A submersible pump also has a great runtime as it is cooled by the surrounding water.

Heating The Pond in The Winter

If you are from a cold climate and everything around freezes, you will need to heat the pond. Some of the pond fish can thrive below 0 degrees but most of them won’t.

There are a number of ways to heat a pond in winter. But for a small pond using a de-icer or immersed heater is the best practice. It saves a lot of money.

A deicer doesn’t heat the pond, rather it floats around and keeps an air hole. Thus both fish and bacteria can thrive in the winter.

An immersed heater will keep the pond water temperature constant. Hence, you should use this one if you have fish that can’t thrive at low temperatures.

What Fish Can You Stock in Small Pond


Goldfish will be the best pond fish for this size pond. Common goldfish can live for 10-25 years in a well-maintained pond. Although fancy goldfish are also available, I don’t recommend you stock them in your pond. They are good in the aquarium, not in a pond.

If your pond is at outdoor, don’t stock very little goldfish, they may die soon. Goldfish are very friendly and you can stock them with other pond fish like koi.


When we say garden pond, we mean Koi pond. Koi’s are a favorite garden pond owner for centuries.

As the depth of your pond is less, you shouldn’t stock large koi in it. Again large koi are expensive too. It is recommended that you don’t stock koi larger than 10 inches in a small pond. If you want to stock large adult size koi, our pond depth should be at least 3 feet.

You can buy small koi fish on amazon or PetSmart cheap.

As koi grow quickly, you may need to transfer them to a larger size pond within a year.

Other Small Fish

Apart from koi and goldfish, there are other small fish that you can stock in your pond. Some of the good small pond fish are –

  • Mollies
  • Guppies
  • Red Shiners
  • Plecostomus
  • Siamese Algae Eater
  • Pond Loach

How Many Fish You Can Stock in Small Pond?

The number of fish you can stock in a 100-gallon pond depends on the species and size of the fish. If you stock Mollies and Guppies the number will be higher than the Koi.

  • You can stock up to 3-4 medium size koi in 100-gallon water. Anything more of that will make it overcrowded.
  • If you stock baby koi of 2-3 inches long, then the number will be 60-80. But you should stock less as they grow quickly
  • One Goldfish requires 20 gallons of water. Therefore you can stock 5 of them in 100 gallons.
  • You should never stock an adult koi in a 100-gallon pond.

It is better to stock a blend of fish. Stock 15-20 small baby koi, 3-4 goldfish, and 20 other smaller size fish in 100 gallons. For a 150 and 200 gallon pond, the number will be 1.5 and 2 times 100 gallons or less.

1 thought on “100, 150, 200 and 300 Gallon Small Koi Pond The Ultimate Guide”

  1. 20 years ago, my son built a deck, bridge, and walkways that surrounded a hand excavated pond. It was such a delightful surprise. Eventually, for about 10 years the goldfish, koi, and frogs were sustaining a healthy, balanced ecosystem. I no longer had to provide commercial foods. Unfortunately, due to development encroaching throughout wildlife habitats, a Blue Heron showed up in 2010 and it dessimated my pond. As the fish were killed, so were the mini nurseries for the members of my pond. Then an invasive plant, probably planted by birds took over. I lost control of my sanctuary. The pond failed and has about 6 inches of water in the deep end–varying because of rain. I put Dunk cubes there to control the mosquitoes.
    My son used a pool liner and a swimming pool pump. I incorporated UV lights, filters, and aeration techniques to try to rebuild the pond. It had a waterfall with the correct rise and run. My son was a surveyor. He built it as a kidney shape. The main part was about 10 X 20, 2/3 =2 feet deep, the other third, 3 feet deep, and then the shallow portion was where the falls emptied, 6 X 8 feet, 1 foot deep, under a bridge, with nooks and crannies for the nurseries. So, I guess the pond had a capacity of approximately 650 gallons. A rainy season could increase it to 800 gallons. During its highpoint, the fish wintered over in the deepest section. Dragonflies used to hover around and I loved going to sleep to the songs of the frogs…most is empty and all is silent.
    I still have the basic outline and most of the depth needs to be refined. The liner needs to be stripped out, the rocks need to be removed and cleaned, and that “trailing plant” eradicated. It flourishes in soil and water. I used to joke with my granddaughters about weeding the pond every summer.
    Now I don’t know what to do. My son suggested that I fill it in and carry on. I live in Fayetteville NC which is zone 8a.
    I sincerely hope you won’t respond with a canned message out of an SOPM. I really would like to hear your feedback on how I can perhaps downsize the project and make recommendations regarding equipment and successful sustainability.
    Thanks for your interest in my situation

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