When constructing the goldfish pond, you need to choose what size you want the pond to be.
There are certain size constraints you should definitely abide by, such as depth of at least 3ft to prevent freezing and having a large surface area to provide better gaseous exchange within the water body.
However, the length and width can vary depending on a few things, these include:
- Amount of goldfish
- Filtration size
- Cost of running and setting up
- What breeds of goldfish you want to keep
The volume of water is just as important as the space provided for your goldfish, as the amount of water a pond can hold contributes to its water quality.
A pond with a relatively low volume of water means that it will become polluted with nitrogenous waste much faster.
Contrary to what some may think, more water actually means less maintenance not more, as it takes much longer for water quality to deteriorate in a larger volume.
This makes calculating the volume of water in your pond important in deciding how many fish you want to keep, as more fish means more food, more waste and more ammonia.
What is a good size for a fish pond and how many goldfish can I keep?
A single full grown goldfish can live in a pond equivalent to 75 gallons (imperial), or 3ft x 2ft x 2ft.
However, goldfish are social creatures, and need to be kept with more of their own kind – the more goldfish in the group, the more comfortable they will feel.
A good starting number for a school of goldfish is around 5-7 so by this, we can consider the size requirements for each goldfish.
To calculate this, a good rule to go by is:
75 gallons (imp) / 90 gallons (US) for the first goldfish, and then an additional 20 gallons for each additional fish.
For a school of 5, the volume of water should ideally be around 150-170 gallons(imp) or 190 gallons (US).
As always with fish, the larger the volume of water the better quality of life you are providing them.
Space for breeding goldfish
If you wish to breed your goldfish, try to provide a little more space than usual, as part of goldfish courtship is to chase each other around at high speeds and drop their eggs amongst plant life or shale where they may survive.
Goldfish can become very irritable during spawning season, so plenty of space should be allowed for them to avoid one another if they become too stressed out.
When housing goldfish long term, unless you have a confirmed place to move them when they grow up, you need to know the full size they will grow and attribute this to your stocking level and selection of goldfish breeds.
Fancy goldfish tend to be much smaller than the typical comet or shubunkin (which can exceed lengths of 10”) so you may have a smaller pond, but be aware that fancy goldfish do not fare well in winter and may need to be brought inside during months of harsh inclement weather.
Also remember that as the amount of goldfish increases, the amount of filtration you will need to keep the water biologically “sound” will also increase.
Overcrowding causes stress, fowls water quality quickly, and can lead to many health problems down the line which can kill your goldfish.
If you are new to pond keeping, be modest with the amount of fish you house in your pond, 5 or 6 is best to start with, especially for those smaller ponds.
Calculating the volume of your pond
If you are buying a pre-formed pond mould, the volume of water that it holds should be made clear on the packaging. If not, then there are ways of calculating it yourself – this is a very useful skill to have, especially if your pond is an atypical shape.
If you are building a pond with concrete or a liner – and can therefore choose your own goldfish pond size – then you can work out what volume of water it will hold by following this simple rule:
- Measure the volume of the pond in cubic centimetres by multiplying the length and width in cm by the depth in cm.
- Divide this amount by 1,000 to give you the volume in cubic litres.
- Then divide this number by 4.5 in order to give you the goldfish pond size in imperial gallons. or divide the literage by 3.8 for US gallons.
Remember, you won’t be filling your pond right up to the brim, so make sure to knock some volume off for the gap you leave at the surface.
Goldfish and carp are fish which originate from cold lakes and rivers – this means that their bodies are used to having consistent, high oxygen levels.
A large pond surface area is imperative in ensuring the pond can perform gaseous exchange effectively.
Similarly, plants need good surface area, as they feed on Co2 which dissolves in the water from the surface. Without good surface area and oxygenation, your plant and animal pond inhabitants will suffer.
Additionally, to improve oxygenation, adding a waterfall or high surface agitation has a dramatic positive effect on pond life.
How deep should a goldfish pond be?
Fish are cold blooded animals, and this means they must regulate their body temperature through their environment.
Having a pond deep enough is vital in allowing goldfish to control this – the depth of a pond is what allows fish to escape from the heat of the sun, and the bitter cold of the wind and ice.
To allow fish to escape freezing temperatures and other harsh weather, the pond needs to be at least 3ft or 36” deep.
Depth also changes the environment of the pond, and the deeper parts will contain less oxygen.
A deeper pond may require further surface agitation to increase the oxygen level, or add a current to the pond with a pump/filter to circulate the oxygenated water to the furthest reaches of the pond.
How to prevent overcrowding
Preventing overcrowding can be as simple as choosing to put less fish in the pond when you initially set up. Try to stay within your pond’s ideal boundaries, as discussed before, goldfish need a good amount of space to live in and stay healthy.
Selecting a good filtration system can assist with heavily populated ponds, more fish means there is more waste being produced; this is what is known as “bioload” and this increases with the number of animals living in the pond.
A high bioload needs a higher level of filtration to manage and keep down harmful ammonia and nitrites.
Long term, an issue you may run into in a healthy, established pond is having your goldfish breed naturally. In the UK, breeding occurs in early spring and autumn.
In natural ponds with plenty of plants, stones and cover, some of the spawn will survive and you may gradually end up with more and more fish.
If your pond cannot accommodate more fish from the ones you already have, then it may be best to:
- Catch some out and move them to a different pond
- Give them to a friend or family member
- Try asking your local aquatics store to see if they can take them (some places will offer store credit for your fish)