Daft question but......

[smithy29]

When you do a water change is it cold water or warm water

 

[Fishmanic]

you should try to match the temperature of the makeup water to the temperature of the tank water as close as possible

 

[Colin_T]

In addition to Fishmanic's response, if you have a tropical (warm water) aquarium, you try to use warm water for water changes. If you have a cold water aquarium, then you add cold water.

You can add some boiled water to a bucket of cold water to increase the temperature for a tropical tank, or just use a bit of hot water from the tap to warm up the bucket of new water.

You want the new water to be a similar temperature to the aquarium water. It doesn't have to be exact, just have it within a couple of degrees. If you stick your finger in the water and it feels similar to the tank water, then it is fine.

Try to aerate all new water for at least 5 minutes (preferably 30 minutes) before adding it to the tank. This allows the gasses in the water to get back to normal and also allows dechlorinators to come in contact with all the chlorine/ chloramine in all the new tap water in the bucket.​