How to Prepare Brackish Water for Guppies

Sand is a good choice for brackish aquariums.

Sand is a good choice for brackish aquariums.

Tired of boring freshwater aquariums? Move your guppies to a brackish tank. Guppies do well in freshwater aquariums, but their natural habitat is brackish water. Brackish water is part fresh and part salt, naturally found in swamps and estuaries, and easy to recreate at home for your guppies.

Choose a tank suitable for brackish water. Glass and acrylic aquariums are acceptable, but tanks with metal frames, thermometers, hoods or other accessories are not. You'll also need a hydrometer for measuring the gravity of your tank.

Fill a large plastic bucket with enough tap water to fill your tank. If your tap water is treated with chlorine, you'll need to condition it before adding salt.

Mix in the proper amount of marine salt for preparing brackish water, per the manufacturer's directions. Freshwater aquarium salt and table salt are not good choices, according to Fish Channel. You can pick up marine salt at most aquarium retail stores.

Stir the water until the salt fully dissolves. Depending on the amount of water and its temperature, this may require several minutes of continuous stirring.

Test the gravity of the water to ensure you've added the correct amount of salt. Brackish water has a density of 1.003 to 1.010, and guppies prefer water density on the lower end of that scale. Adjust as necessary.

Transfer the salted water to your tank. Pour the water very slowly to prevent splashing.

Cycle the tank water and then check the gravity, temperature and pH of the water before introducing your guppies. Guppies tolerate water pH of 6.8 to 7.6, but they prefer 7 to 7.6.

Items you will need

  • Glass thermometer
  • Hydrometer
  • Large plastic bucket
  • Chlorine conditioning tablets
  • Plastic spoon
  • Marine salt
  • Water pH testing kit


  • If transitioning a freshwater tank to brackish water, prepare the brackish water in a plastic container and then replace 25 percent of your tank's existing water with the brackish water. Repeat this process once each week until the tank reaches the ideal gravity.


  • Salt will rapidly corrode metal. Avoid the use of metal accessories and tank parts.
  • Be careful when choosing other fish for your tank; not all fish can tolerate brackish conditions.

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Sandra Ketcham has nearly two decades of experience writing and editing for major websites and magazines. Her work appears in numerous web and print publications, including "The Atlanta Journal-Constitution," "The Tampa Bay Times," Visit Florida, "USA Today," AOL's Gadling and "Kraze Magazine."

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