Cyclic Tasks: Water Changes

Table of Contents

This article is part of the “Cyclic tasks” series, intended for beginner aquarists who are looking for the basics of running a saltwater aquarium, or for those who are considering setting up a tank and want to understand the amount of work involved.

In order for the aquarium to function properly, we must regularly undertake certain works. If you’re a beginner aquarist, you’ve come to the right place!

Things necessary to prepare brine

  • An appropriately sized bucket or container
  • Heater
  • Safe circulator (we must be sure that the powerhead does not release anything into the water, i.e. that the rotor does not rust or its other metal elements do not release undesirable substances into the water)
  • Salt
  • Refractometer and calibration liquid
  • Scales
  • RO water

Preparation of brine for replacement 

In an aquarium, we usually replace 10% of the volume of the aquarium capacity. So if we have a 200L aquarium, we will do a change of 20L of water.

Pour RO water into the bucket. Then insert the heater and the circulator. We heat the water to the same temperature as we have in the aquarium – usually it will be 25 ° C / 77 ° F. Then, weigh the appropriate amount of salt (according to the manufacturer’s instructions from the packaging), select the weight for the given salinity. Our goal is that the brine in the bucket has the same salinity as the water in the aquarium. Pour the salt into the bucket.

The water is getting mixed. Ideally, such water should be mixed for at least 24 hours. This time will allow the chemistry contained in the salt to combine properly in the water, and unnecessary ingredients will oxidize.

After mixing, we check the salinity with a refractometer. If it deviates from the goal, we add salt or add water to our bucket. Remember that the goal here is to have the same salinity we have in the aquarium. Let’s not forget about the same temperature as well.

We remember that after adding salt, it should be closed tightly.

Preparation of utensils for water change

To perform a water change we will need:

  • Hose
  • A bucket of the right size to drain the water from the aquarium
  • Water in a bucket with previously prepared brine
  • A cloth or other material for wiping wet surfaces
  • Refractometer and calibration liquid

Performing a water change

  1. Stop the aquarium (turn the water circulation off)
  2. Using a hose, we drain the right amount of water (exactly the same amount as we will pour into the aquarium)
  3. Pour water into the sump or aquarium (if we have room for additional water in the sump, it is better to add it there, and if there is no spare space, we add water to the display tank)
  4. Start the water circulation
  5. Wipe up any spilled water
  6. Pour the water drained from the aquarium into the sewage
  7. Store the utensils


Water changes are a permanent element of works on a marine tank. The subject itself is not difficult, as usual, it’s about getting used to it and following a few simple rules.

Thank you for your attention 🙂 I encourage you to read the next articles, because expanding knowledge in our hobby is essential.

About the author

Picture of Marek Protasewicz

Marek Protasewicz

Reefkeeping has been my passion for over 10 years now. I love learning. The hobby has taught me many valuable lessons, patience being the best example. Combining work and passion is my path. I run Crazy Coral, a marine aquarium shop, for a number of years. Building this business from the scratch I learnt from my own mistakes at a heavy cost.
Later I managed a project aimed at development of methods for quick growth of Corals in non-natural conditions. The project was carried out by Get Sales, Poland. Presently, I am responsible for distribution strategy at Reef Factory, of which I am a co-founder. The company produces smart devices for marine aquaristics. The last projects I have been involved in are Social Reef and ReefPedia.

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