The Aquarium Water Change

Topic Overview

Regular water changes are the most important part of maintaining an aquarium. Because it’s such a simple task, the ‘dos & don’ts’ are often overlooked.

It’s routine, it’s mundane, it doesn’t always fit into our schedule. Yes, we are talking about the aquarium water change.

What do you need for the task? For all practical purposes, a simple bucket or pot will do the trick. Scoop out some water, pour fresh water back in …after using a conditioner of course… Bingo, you did a water change.

Ok, so maybe that’s not our best option for changing water. Let’s take a look at some of the variables, so we can get the most bang for time spent.

Getting the Most Out of the Aquarium Water Change

Maximizing the benefits of the water change

Organic waste accumulates and dissolves in the aquarium, as a result nitrate is constantly created. Because nitrate is the final nutrient in the nitrogen cycle, our best option is to physically remove it through regular water changes.

Because the aquarium is a closed-loop ecosystem, accumulating waste and nutrients must be regularly removed through water changes.

To maximize the benefits of your water changes, always use a siphon to ‘vacuum’ the gravel while extracting water. Removing waste settled at the bottom of the tank is extremely beneficial for maintaining a healthy and balanced aquarium.

Regularly scheduled aquarium water changes include these benefits:

  • Removes accumulating nitrates
  • Waste particles settling at the bottom of the aquarium can easily be removed with a siphon
  • Removes toxins and chemical pollutants
  • Improves water clarity and removes odors
  • Adding fresh water back into the aquarium increases available oxygen
  • Replenishes depleted minerals and trace elements

Recommended Aquarium Water Change Schedule

The benefits of regular water changes

Our recommendation for general aquarium maintenance purposes

  • Weekly water changes of about 10% of the tank volume.
  • Optionally, 15 – 20% every other week, works in most aquariums as well.

Using these weekly and bi-weekly guidelines, the schedule can be tweaked to suit each unique aquarium setup. In some cases less frequent water changes will work, while heavily stocked aquariums likely require more frequent changes.

Some trial and error is required to determine the most effective water change schedule for your own aquarium.

Additional maintenance tasks at the time of water changes

Inspect of the filter and filter media. If the filter is dirty, usually a quick rinse with fresh water will do.

Filter inserts may also benefit from a quick rinse. Generally they do not need changed at the same frequency as water changes are completed.

What to avoid when changing water

Occasionally we experience deteriorating water conditions, an algae outbreak, or green aquarium water. It is important to take measured action, when attempting to correct these problems.

A common overreaction is to go BIG. It is tempting, and even seems sensible, to change nearly all the aquarium water. Furthermore, thoroughly cleaning the filter, and replacing all filter media is not always helpful. Only on rare occasions is such drastic action recommended.

The result of these actions, individually or combined, can lead to a severe decline in nitrifying bacteria. When you decrease the population of this beneficial bacteria, the result is a disruption of organic waste breakdown in the aquarium.

Ultimately this can lead to worsening tank conditions, including a rise of water toxicity from increases in ammonia and nitrite, more severe algae outbreaks and dense green aquarium water. 

Good intentions can lead to excessive action, resulting in an unbalanced and toxic aquatic environment.

General Aquarium Water Change Guidelines

  • Water temperature should be +/- 5 degrees F of the tank water
  • Use a water conditioner. Fresh water added to the aquarium should be free of chlorine, chloramine, and heavy metals (lead, copper)
  • Never use hot water to adjust the temperature inside the aquarium. It can severely shock fish. Furthermore, older hot water tanks may contain toxic levels of zinc
  • If using tap water, let the water run for a minute to clear the lines of possible dirt particles
  • Know what you’re adding to your fish tank! Check tap water check for nitrates. More importantly make sure the pH and kH match that of your aquarium

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New fish keeper🐠

Hello! I have a question. So i’m a beginner at fish keeping and I’ve read somewhere else that you should do 100% water changes. I’m guessing from this article that isn’t true. So i’m just wondering what I should do if I just want to clean the gravel and the ornaments inside my tank. I read that you should clean them with hot water. I’m just wondering how do I do that? Do I just get the gravel out and the ornaments? Like I said i’m a beginner at fish keeping and I wanna be really prepared before I get… Read more »


You can use a siphon to vacuum the gravel, this will remove waste and is the best way to perform water changes. Gravel provides benefits, one of them is space for bacteria to grow which will help to keep the water safe for the fish. Therefore, gravel should not be washed. Ornaments can be removed and scrubbed if necessary, hot water and a sponge. Do not use soap.

J. Hargett

I change half the water in my 50 gallon tank every three weeks using the Anaconda suction tube. That has worked perfectly for me and my 20 community fish. Some might say it’s too much water, but it takes time to vacuum the entire gravel bottom.


Is there a frequency of changing all the water and cleaning everything in the tank? I’ve had my tank a little over a year and all is well and I do the 20% water changes every two weeks.

You should never change all the water in the aquarium. Bi-weekly water changes of 15 – 20% of the water is a good schedule for water changes.

If you were to change everything, it would be like starting all over again and your tank would no longer have the necessary beneficial bacteria need to breakdown waste in the fish tank.

Please see the following articles for more information as well as our aquarium maintenance recommendations here.

First aquarium
Nitrogen cycle
Biological filtration

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