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Is Hard or Soft Water Better for Fish?

Is Hard or Soft Water Better for Fish?

Asked By: Alex from Sanders, AZ

A: The answer depends on what types of fish and invertebrates you are raising. Some fish species prefer soft water, while others thrive in hard water.

Start by measuring the parameters of your pond water with a test kit and ascertaining what types of fish live in your pond. Testing enables you to make changes to ensure the water is perfectly suited for aquatic life to thrive.

While most fish can survive in a wide range of water conditions, the ideal water hardness for your finned (and shelled) friends also depends on which treatments you use in your pond. If you apply herbicides or algaecides containing copper or zinc, the minerals in hard water can help protect your fish from metal toxicity.

Hard Water Fish

The following aquatic critters do best in hard water(between 100–250 mg/L )with ample dissolved minerals:

  • Koi
  • Goldfish
  • Guppies
  • Trout
  • Bass
  • Crustaceans
  • Mollusks

Soft Water Fish

These fish species prefer soft pond water (between 50–150 mg/L) with fewer minerals:

  • Plecostomus
  • Bluegill
  • Loach
  • Catfish
  • Most spawning fish

Balancing Water Parameters for Your Pond Fish

After you conduct a test, you might need to adjust your pond water for your fish or relocate them to a more suitable habitat.  Contact us online or by phone at 866-POND-HELP to learn how to harden or soften pond water to keep your aquatic pets happy.

Read more water quality tips below:

How to Lower pH in a Pond

Carbonate Hardness in Pond Water

How to Do a Jar Test

How to Create a Fish Spawning Habitat

Last Updated: January 14, 2025