How to Keep Koi Fry Indoors: A Winter Aquarium Project Guide

We love hearing about how koi can bring enjoyment throughout the entire year, not just during the warmer summer months!

One of our customers recently shared some wonderful photos of a batch of our Round 2 fry thriving in a beautifully decorated indoor aquarium.

Carl, a dedicated koi keeper, says, “We’re keeping the koi fry that you supplied indoors in two aquarium tanks at 23 degrees. They’re growing so quickly! With the help of an external filter and regular weekly water changes, we’re able to keep the water quality in excellent condition.”

Carl goes on to share more about their fascinating behaviour: “The koi are very inquisitive and love to explore anything new, whether it’s an extra plant or a piece of filter pipework. Watching them interact and grow week by week has become one of our favourite pastimes—we often find ourselves sitting there, completely captivated by their activity.”

Supporting our customers in discovering new ways to enjoy koi keeping is one of our greatest passions. Raising koi fry in an indoor aquarium over winter is a lesser-known but highly rewarding project. With the right setup and careful attention, you can watch these incredible little fish flourish right in your home. And there’s something special about observing koi up close in this setting—their vibrant colours, curious personalities, and interactions with each other truly shine indoors.

If you’re thinking about starting your own winter koi project, here are a few tips:

Temperature and Water Quality: Maintaining a steady, temperature and consistent water quality is key to keeping indoor koi healthy. External filters and regular water changes help manage both.  Koi in an indoor tank don't require a heater - the ambient temperature indoors will be more than sufficient for them.  If you wanted to heat the tank, 23C would be ideal.

Creating an Enriching Environment: Koi fry love to explore, so adding variety like rocks, artificial plants, or even harmless decorative items can encourage their natural curiosity.  Koi will eat natural plants, but that's not a problem as there's such a great range of artificial plants available now.

Bonding Time: Indoor koi care provides a unique chance to bond with your fish. Spending time by the tank helps you get to know their individual behaviours, and it’s a fantastic way to relax!

If you’re already keeping koi fry indoors over the winter, we’d love to hear about your experience! And if you’re just getting started, feel free to reach out to us for advice on setting up the ideal indoor space for your koi. While keeping koi indoors is typically a short-term project—these little ones grow quickly and will soon need a larger home—starting them indoors over winter and then transitioning them to an outdoor pond in spring allows you to enjoy watching your koi thrive throughout the year. We’re here to help you make the most of this rewarding journey!