How to Change the Water in a Saltwater Fish Tank

As anyone who has kept fish knows, water changes are an essential part of keeping your aquarium clean and your fish healthy. Though typically a fairly straightforward task, changing the water in a saltwater aquarium can be more difficult. It requires an extra degree of care because marine fish are far more fragile than their freshwater brethren. Follow these steps to ensure that you change the water properly and avoid harming your aquarium's inhabitants.

Things You'll Need

  • 2 buckets
  • Aquarium sea salt
  • Mixing spoon
  • Cup
  • Hydrometer
  • Dechlorinator
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Instructions

    • 1

      Fill one of the buckets with fresh water.

    • 2

      Bring both buckets, the one filled with water and one empty, to your saltwater aquarium.

    • 3

      Measure the specific gravity of your aquarium water with the hydrometer and make a note of it. With most hydrometers, you simply need to dip it below the aquarium water's surface until it fills. Then place it on a flat surface, where it will work like a gauge with a tiny needle that points to the specific gravity clearly labeled around the edge of the device. Most saltwater aquarium water has a specific gravity of about 1.022 parts per trillion.

    • 4

      Pour some of the aquarium sea salt into the bucket of fresh water and mix it around until it dissolves completely.

    • 5

      Measure the specific gravity of the water in the bucket using the same hydrometer. Make sure to clean the hydrometer by rinsing it out with fresh water beforehand.

    • 6

      Adjust the salinity of the water in the bucket until it matches the salinity of the water in your tank. You can adjust the salinity by either adding salt (to raise it) or by diluting it with fresh water (to lower it).

    • 7

      Pour 1 cup of water from your aquarium into the empty bucket.

    • 8

      Take the same cup and use it to replace the water you just poured with the new saltwater you just mixed in the other bucket.

    • 9

      Repeat steps 7 and 8 until you have changed approximately 25 percent of the water in the aquarium. You may need to make up another bucket of new saltwater is you have a larger tank. Do not change any more than 25 percent of the water within two weeks' time.

    • 10

      Add the appropriate amount of dechlorinator into your aquarium. This liquid will eliminate chlorine and other dangerous chemicals, particularly from the new water you just added to the tank. Consult the dechlorinator's package for instructions. Only add the amount that is appropriate for the amount of water you added to the tank.

    • 11

      Dispose of the old water by pouring it down the drain.