Water Preparation for Fish in an Outdoor Pond

Early spring is the ideal time to add fish to a filtered outdoor pond because the weather is mild and the newly-introduced fish have six to seven months of warm weather to settle in before the winter.

  1. Water Preparation

    • An established rainwater pond requires little preparation before adding fish, but if the water has come from a domestic supply, it will contain chemicals that are harmful to fish. Add a broad spectrum "pond safe" water treatment to remove chlorine deposits to make it suitable for fish and a "bacteria booster" to kick-start the natural waste processing system required for a healthy ecosystem within your pond.

    Pond Size and Fish Stock

    • Measure the volume of your pond and work out realistically how many fish it can handle using an online pond volume and fish stock calculator (see References). An overstocked pond jeopardizes the health of all your fish, so never add more than the recommended quantity.

    Choosing Fish

    • Goldfish are great starter fish as they are hardy and over-winter well. Koi carp, shubunkin and golden orfe also have the same environmental and dietary requirements, so a mixture of these will look attractive and be simple to maintain.

    Introducing the Fish

    • Introduce new fish to your pond in batches of two to three per week, allowing the pond filter and water to acclimate to the increase of waste products gradually. If you add all the fish at once, the filter bacteria will not be able to cope, and ammonia, nitrate and nitrite will build to dangerous levels and kill the fish.