The most important aspect of fishkeeping because it involves the removal of fish waste (specifically but not just including nitrates). It is the equivalent of changing the bedding of other animals but where fishes waste is all around them it is very important.

Frequency and Volume

This will vary and can be anywhere from weekly or daily. The minimum I’d recommend is weekly 25% on a lightly stocked aquarium but the more frequently the better. If concerned about temperature changes then preheat the water with a heater in a jerry can or leave it to rise to at least room temperature. Spreading those water changes across the week can be an answer although not suitable for everyone, so instead of say 50% once a week 25% twice a week will remove the same amount.

It is not uncommon for those with discus to water change 50% every other day or with goldfish to do daily 50% or even 100% water changes.

Where fish might be kept seasonally this means water changes will vary seasonally along with a reduction in feeding during the winter or dry season. Goldfish and other fishes kept outside where temperatures reduce 15c or lower over winter may go without feeding or water changing during those winter months when temperatures can dip to around 5c.

What is needed?

This depends on what you want to water change with so you can change things up a bit.

• Water conditioner, to remove chlorine and chloromines from the tap water. Not required if using RO water (refer to our file on the use of Reverse Osmosis within freshwater fish), a HMA filter or rainwater (refer to our unit on rainwater).
• Tubing, hosing or aquarium tubing. The length depends on where you plan on sending waste water to whether it be a sink, bath, garden or a bucket.
• (Optional) Bucket or jerry can, if waste water or new water is going to be carried with a container.
  • (Optimal) Water pump if wanting to pump the water from a container to the tank.
• (Optional) Tap connectors, Hozelock does a few models. This is useful if supplying the new water to the tank direct from a tap, add water conditioner beforehand.
• (Optional) Python is piping with a series of connections allowing to water change to and direct from a sink.

The Process

Emptying the water is often done by siphoning although can be done with a pump. There are multiple ways to start the flow of the siphon from sucking on the tube quickly or lowering the tube into the water, best researched and watch different methods and there is no one way to do it.

Once the volume requires is removed then the new water must be added. Any new water from the tap even if it is to be mixed with RO or rainwater should be dechlorinated before entering the aquarium. Dechlorinating can be done straight to the aquarium if filling with a hose or to the buckets/jerry cans if doing it that way.

Why?

Whenever thinking about a topic you’ll always need to think of why. Putting it simply water changes remove excess waste from the fishes, much of what can’t or wont be removed by plants. In addition to removing, water changes replenishes many vital vitamins and minerals, if curious into that topic more please read this page discussing minerals and fish biology.