We often hear about how goldfish are hardy fish that can survive a wide range of water conditions – including very cold and quite warm water – but are some temperatures more suitable for goldfish than others? How hot is too hot? How cold is too cold? And what temperature encourages goldfish to breed?
Read on to find out how best to measure your goldfish tank temperature, the right temperatures for breeding goldfish, non-breeding aquarium temperatures, and the importance of air supply in warm water.
How to measure tank temperature
To measure your tank temperature you will need to purchase an aquarium thermometer and follow the instructions. As you can see on Amazon, there are types of thermometer that stick to the inside your tank and types that stick to the outside of your tank. We prefer the ones that go inside and float in the water, but both types should be reasonably accurate.
Breeding tank temperature
The correct temperature for goldfish really depends upon whether you intend to breed your fish.
If you intend to breed your goldfish then, rather than maintaining a steady temperature all year round, you should try to replicate the temperature changes that occur in nature. Goldfish spawn in the spring, when water temperatures rise after the cold winter. Therefore, to encourage your goldfish to lay eggs, you should lower the temperature of your tank in the winter months to between 10°C/50°F and 12°C/54°F. Then, when you want to induce breeding, gradually raise the temperature of the water to between 20°C/68°F and 23°C/74°F.
Non-breeding tank temperature
If you’re not interested in breeding your goldfish then you should keep your temperature at a steady temperature all year round. A tank temperature of approximately 23°C/74°F will be high enough to encourage a good rate of growth in your goldfish, without being so high that your goldfish become stressed.
How hot is too hot? And how cold is too cold?
Your goldfish will become very stressed if kept in water of 30°C/86°F or more. Avoid placing your tank in direct sunlight or near radiators so that your water temperature stays well below this level.
In terms of a minimum temperature, goldfish can survive in water that is close to freezing, however, you should really keep your tank temperature several degrees above this in order to encourage strong growth.
The most important thing is that your tank temperature does not change suddenly. Sudden changes in water temperature can shock your goldfish and contribute to problems such as swim bladder disease.
It’s important to realize that the hotter your goldfish’s water gets, the less oxygen there is in the water. Of course, goldfish need oxygen to live, so you must ensure that your tank has an adequate “aeration system” (a system of adding air into the water). We recommend buying a tank that has a large surface area – avoid “tall” tanks that have a poor surface area to volume ratio – and adding an air pump.