How Many Fish Can Your Pond Hold?

If you are building a new pond or are thinking of adding to your existing one then it is worth calculating how many fish it can hold. An overstocked pond can cause unhappy fish, even death in some cases, which causes extra work. There are a few measures that you should take to prevent overcrowding and to mitigate the effects if you do find your fish are suffering due to a lack of space.

How many fish can I have for my capacity?

There are a couple rules that you can follow when it comes to calculating your pond capacity. If you are keeping koi, you should allocate 35 gallons per inch of fish if you are keeping goldfish this should be 20 gallons per inch.

 A second rule is to have 1 square foot of surface area per inch of fish and 10 square feet of surface area for 1 koi. So, as an example, if you have a pond that has a capacity of 2000 gallons, you can hold 57 inches of koi fish (5 domestic koi fish) and 100 inches of goldfish (25 common goldfish).

Calculating capacity (gallons)

Square or rectangle pond: length x width x average water depth (feet) x 7.5

Round: diameter x diameter x average water depth (feet) x 5.9

Causes for overcrowding

More often than not, overcrowding of a pond is a genuine mistake. Fish grow and it can be hard to tell exactly what size they will reach, especially Koi, in addition to your fish breeding at a rate that is difficult to control

The dangers of overfilling

Having too many fish is a ticking time bomb. Too much going on in the water can encourage the spread of parasites because your filtering system might not be able to keep up with the amount of organic waste from your fish. Furthermore, levels of ammonia can become too high if it is overpopulated, which naturally increase during the summer and can cause a loss of fish.

Furthermore, it reduces the likelihood of your fish breeding successfully.  Fish without enough space to move and explore can become unhappy, lose their vibrant colours and their appetite. If you are a koi owner, one of the joys is feeding them which will quickly loose its appeal if your fish are not hungry or happy. Not only does this make your fish distressed, it can increase the stress of managing your pond, making it more of a chore than a hobby.

How to prevent overcrowding

When calculating how many fish your pond can safely hold make sure you consider how much your fish might grow over the coming months, especially if you are keeping domestic koi which can grow up to 12-15 inches, Japanese can grow up to 26 inches. You also need to leave some of your capacity free In case your fish begin to reproduce. If you feel like your pond is suffering because of the number of fish you have, then upgrading your filters and pumps will improve the conditions of the water. A larger filter will be able to filter more litres of water per minute and keep up with the amount of filtration required. A larger pump, air stones or a fountain will create more oxygen in the water, preventing dead spots.

An overstocked pond also encourages algae. A green water treatment will help to improve the quality of the water in your pond, giving your fish a healthier environment to live in.

However, if your pond is overcrowded beyond treatment, you will need to remove some of the fish. You can do this by giving them away to friends or family who keep fish or sell them, but only if you are sure that your fish will be safe in their new environment.  Alternatively, you can check whether any local pet stores or aquatic centres accept second-hand fish, but by any means do not release them into a river or a lake. Alien species to the natural eco-system can cause harm and once an alien species becomes accustomed to their new eco-system it is almost impossible to reverse the effects.

For more information or advice about stocking your pond, or additional equipment that may improve your water quality, our support team are on hand to help. You can contact our Customer Service Team via our support centre