How to Mix Saltwater for an Aquarium?

Setting up a marine aquarium or changing the water in an already established tank involves the crucial step of mixing saltwater, essential for ensuring the well-being of aquarium inhabitants. While the process of mixing salt with water may seem straightforward, it should be executed with particular care when it is intended for your aquarium.

This article will guide you through the entire process.

How to Mix Saltwater for an Aquarium?

Get your supplies

To begin, buy a high-quality salt mix specially formulated for aquariums. Purchase the mixture from a reputable manufacturer, such as Aquaforest, known for high-quality marine aquarium equipment and supplements. Ensure you have an adequate amount of salt to match the water volume in your aquarium.

The process also requires high-quality water, which varies depending on the type of aquarium:

  • For fish-only aquariums, use dechlorinated water;
  • For reef tanks, you will need reverse osmosis and/or deionized water.

Other essential supplies include:

  • A clean container for mixing water and salt;
  • A reliable thermometer;
  • A submersible aquarium heater;
  • A small pump for water circulation;
  • Either a refractometer or hydrometer for measuring specific gravity and salinity.

Preparing the saltwater

Rinse the container without using any detergents and fill it with water, avoiding filling it to the top. Set up the powerhead and heater to speed up salt dissolution and maintain the temperature appropriate for your aquarium. Use a thermometer to monitor the temperature.

Follow the manufacturer’s instructions and slowly add the sea salt mixture to the water, aiming to achieve the specific gravity. Adding salt in three separate batches can help prevent overloading the water.

Once the salt is added, test the specific gravity with a hydrometer or refractometer and adjust the level by adding more salt until the desirable gravity is achieved.

It is highly recommended to leave the saltwater overnight before adding it to your aquarium. This time is needed to ensure thorough mixing of the salt and water, as well as to allow the water to reach the appropriate oxygen/carbon dioxide equilibrium.

Before adding saltwater to your aquarium

After the 24-hour period has passed, recheck the saltwater conditions. Measure the specific gravity once more to ensure it falls within the optimal range of 1.020 to 1.024.

Confirm that the temperature of the saltwater matches that of the water in your aquarium by using a thermometer.

Adding saltwater to the tank

Once all water parameters match the standard requirements, you can proceed to add the prepared saltwater to the aquarium. It is recommended to add the water slowly while continuously monitoring its parameters.


It is essential to follow the steps described in this article carefully to properly prepare saltwater for your aquarium. A thriving marine aquarium cannot exist without correctly mixed saltwater.

Never use table salt or unapproved salt mixes, as they can introduce undesirable substances to the aquarium and affect the health of its inhabitants. Only use products from reputable brands like Aquaforest.

Additionally, avoid using detergents to wash the container used for mixing water, as their residues can be harmful to marine life.

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