Most koi handle winter outdoors just fine—after all, they’re basically nature’s floating snowbirds. But sometimes you need to bring them indoors for the season: maybe your pond is too shallow, freezes solid, or looks more like an iced latte than a safe habitat. Whatever the reason, moving koi inside for winter can be an adventure… a wet, splishy-splashy, “please don’t jump out of the bucket” adventure.
Let’s walk through how to move your koi indoors for the winter safely, smoothly, and without soaking the entire house.
1. Decide Whether Moving Indoors Is Necessary
Before you start rounding up your koi with a net like a cowboy herding aquatic cattle, make sure they actually need to come inside.
Your koi may need indoor wintering if:
- Your pond is under 3 ft deep (risk of freezing solid)
- You live in extreme cold regions (think “Canada’s eyebrows hurt” cold)
- Your koi are injured or recovering
- Your filtration can’t run through winter
- You’re upgrading or rebuilding the pond
If your pond is deep, aerated, and maintained, koi usually overwinter outdoors just fine. But when in doubt—especially with young koi—bringing them inside can be a lifesaver.
2. Choose an Indoor Tank Big Enough for Comfort
Koi aren’t tiny goldfish. They’re big, wiggly, water-loving logs with fins. So your indoor winter tank needs to be spacious enough for them to swim comfortably.
Good indoor tank options include:
- Large stock tanks (100–300 gallons minimum)
- Indoor liner ponds or framed pools
- IBC totes (cleaned thoroughly)
- Rubbermaid agricultural tubs
General rule: Bigger is better. More water = more stability = happier koi.
Bonus: big tubs also reduce the odds of your koi launching like torpedoes at the walls.
3. Set Up Filtration — Your Indoor Lifeline
Bringing koi indoors without filtration is like inviting a herd of muddy cows into your living room: things get messy FAST.
Indoor systems should include:
- A strong biological filter (e.g., moving bed, canister, or pressure filter)
- A mechanical filter (to trap solids)
- A pump with enough flow for the tank size
- Additional aeration—air stones are your best friend
And don’t forget the most important thing: cycling your indoor system before the koi move in.
A fully cycled biofilter = fewer ammonia disasters.
4. Add a Heater (Optional but Highly Recommended)
Indoor systems are easier to heat than entire ponds. You don’t have to make it tropical—just comfortable enough to keep your koi stable all winter long.
Suggested indoor temperature: 55–65°F (13–18°C)
You can go warmer if you want your koi active, but warmer water = more feeding = more waste = more filtration work.
Warning: Never let the water chill or swing dramatically. Consistency is key.
5. Cover the Tank (Trust Us… COVER IT)
Koi + stress + new environment = Olympic-level jumping.
You MUST cover your indoor tank with:
- Netting
- PVC frame with mesh
- Greenhouse-style plastic lids
You’ll thank yourself when your koi do NOT land on the floor at 3 a.m.
6. Prepare Your Koi for the Move
Moving koi is stressful for the fish and occasionally traumatic for the keeper (especially when the koi are bigger than your arm).
To prep your koi:
- Stop feeding 24–48 hours before moving (reduces waste during transport)
- Have holding containers ready (koi bags, tubs, or buckets)
- Make sure the indoor tank is fully ready and temperature-matched
Important: Never move koi from warm water to cold. Always match temps as closely as possible.
7. How to Catch and Transfer Koi (Without Chaos)
Catching koi is part skill, part patience, part “please don’t jump over the net again.”
Use:
- A large soft-sided koi net
- A koi sock net (the best tool ever—prevents jumping)
- Calm, slow movements
Steps:
- Guide koi gently into a corner.
- Use a sock net to lift and transfer—never lift koi in a pan net!
- Place koi into a transport tub or bag with pond water.
- Move them indoors immediately.
Koi Tip: They are faster than you think. Much faster.
8. Acclimate Koi to Their Indoor Home
Just like adding new fish to a pond, temperature and water chemistry matter.
Acclimation steps:
- Float the koi (in a bag or tub) in the indoor tank for 10–20 minutes
- Add small amounts of indoor tank water gradually
- Release gently once temperatures match
No tossing, no dumping, no dramatic splashing. Gentle and slow wins.
9. Indoor Winter Care Routine
Koi indoors need consistent care, but it's usually easier than outdoor winter maintenance.
Weekly tasks:
- Test ammonia and nitrite (non-negotiable!)
- Perform small water changes (10–20%)
- Check temperature stability
- Clean mechanical filters
- Watch for stress or parasites
If water is kept warm enough for feeding, feed lightly and choose easily digestible pellets.
10. Moving Koi Back Outdoors in Spring
Don’t rush it. Your koi have been living the indoor spa life, and their metabolism needs time to adjust.
Wait until:
- Outdoor water reaches 55°F (13°C) or higher
- Nighttime temps stabilize
- Your pond filtration is fully running
Acclimate them slowly back to the pond—just like moving them indoors.
Moving koi indoors for winter doesn’t have to be stressful—or catastrophic—if you plan ahead. Choose a big enough tank, cycle your filter, cover everything, and treat your koi like the finned royalty they are.
Preparation prevents panic, and a well-planned indoor setup keeps koi healthy, calm, and safe until spring returns.
Your koi will survive the winter with grace… and probably enjoy watching you slip on wet floors at least once during the setup. But hey—anything for the fish, right?