How do I keep my fish tank warm in winter?

The most important step is ensuring your heater is working correctly and calibrated accurately using a separate thermometer. You can also reduce heat loss by fitting a tight lid to prevent surface evaporation, placing foam or polystyrene matting under the tank, and taping insulating material to the back and sides if the tank sits against an external wall.

What temperature should my aquarium be in winter?

Most tropical fish do well at 24–26°C year-round. The critical factor is stability, not the exact number. A tank holding steady at 24°C is far healthier than one swinging between 26°C during the day and 20°C at night. Temperature swings are a primary trigger for diseases like White Spot (Ich).

How do I protect my aquarium during a winter power outage?

Stop feeding immediately — without a working filter, ammonia builds up fast and fish can survive several days without food. Wrap the entire tank in heavy blankets or sleeping bags, leaving a small gap at the top for gas exchange. If the temperature drops below 20°C, float a sealed bottle of hot (not boiling) tap water in the tank as a temporary heat source. A battery-operated aerator can also help maintain oxygen levels.

Should I feed my fish differently in winter?

Yes. Fish are cold-blooded and their metabolism slows as water temperature drops. Even a 1–2°C drop in winter can mean fish digest food more slowly. Reduce portion sizes and switch to high-quality, easy-to-digest flakes or pellets. If food is still sitting on the substrate after two minutes, reduce the amount further to avoid waste buildup.

How do I check if my aquarium heater is working properly?

Use a separate, independent thermometer rather than relying solely on the heater's dial. If the heater reads 25°C but the thermometer reads 22°C, the heater is either miscalibrated or struggling. Also inspect the glass casing for hairline cracks during water changes — always unplug the heater and wait 20–30 minutes for it to cool before handling.

Is one heater enough for a large aquarium in winter?

For larger tanks, using two smaller heaters is recommended over one large unit. If one heater fails on a cold night, the second keeps the water from dropping to dangerous levels. This redundancy is especially important during winter when heaters are under more sustained load.

Where should I position my fish tank in winter?

Avoid placing the tank near windows, doors, or any source of cold drafts, as these create cold spots in the water even if the heater is running. Also avoid positioning the tank directly in front of heating vents — the cycle of hot blasts followed by cool periods causes temperature swings that stress fish and weaken their immune systems.

Winter-Proofing Your Aquarium: How to Keep Your Fish Toasty

By Live Fish Expert | Apr 28, 2026 | 9 min read

Imagine waking up on a frost-covered July morning to find your house freezing, but your aquarium is a vibrant, steaming hub of activity. Your fish are just as colourful and energetic as they were in mid-summer. This isn't an accident - it’s the result of a winter-proofing strategy that protects your tank from one of the biggest killers in the hobby: temperature Instability.

In this guide, we’ll walk through the five essential steps to insulate your tank, check your gear, and adjust your feeding habits so your fish don't just survive the cold, they thrive through it.

The "Pre-Winter" Equipment Audit

In summer, your heater barely works. In winter, it is the most hardworking piece of kit in your house. If it’s going to fail, it will happen on the coldest night of the year.

Check for Cracks: unplug your heater during a water change and inspect the glass casing for hairline fractures. Ensure you wait 20-30 minutes after turning off the heater for it to cool down.
Calibration: buy a cheap, separate thermometer. Do not trust the dial on the heater alone. If the heater says 25°C but the thermometer says 22°C, your heater is struggling or miscalibrated.
The Redundancy Rule: for larger tanks, experts often use two smaller heaters instead of one large one. If one fails, the other keeps the water from plummeting to dangerous levels.

LiveFish stocks a variety ofaquarium heaters with built-in thermostats that are perfect for replacing ageing gear before the first frost hits.

Insulation: Keeping the Heat In

Standard glass is a terrible insulator. It allows heat to bleed out into the room constantly. To save on your electricity bill and keep the water stable, you need to "wrap" your tank.

The Lid is a Blanket: most heat is lost through surface evaporation. Ensure your lid is tightly fitted. If you have an open-top tank, consider a temporary acrylic or glass cover for the winter months.
The Polystyrene Hack: placing a sheet of polystyrene or foam gym matting under the tank (before you fill it) prevents heat loss through the bottom.
Back and Sides: in extreme cases, if your tank sits against an external wall, it will lose heat rapidly. Tape a piece of aquarium background or even bubble wrap to the back and sides to create an air pocket of insulation.

Managing the "Draft" Zones

Where you place your tank in August might not be where it should stay in June.

Avoid the Breeze: check for drafts from windows or doors. A cold breeze hitting the glass can create cold spots in the water, even if the heater is on.
Ventilation vs. Heating: while you might have the central heating on, avoid placing the tank directly in front of a heater vent. The blast of hot air followed by periods of cooling causes the temperature to "yo-yo", which stresses the fish's immune systems.

Dietary Adjustments - The Metabolism Shift

Fish are ectothermic (cold-blooded). Their metabolism is tied directly to the temperature of the water. Even with a good heater, most tanks drop 1–2°C in winter.

Slow Down the Feed: if your water is slightly cooler, your fish will digest food more slowly. Pushing the same amount of high-protein food as you do in summer can lead to bloating or constipation in species like Bettas and Goldfish.
Quality over Quantity: Switch to high-quality flakes or pellets that are easy to digest. If you notice food sitting on the bottom longer than two minutes, reduce the portion immediately.

The Emergency Power Outage Plan

Winter storms often bring power cuts. If the power goes out, your filter stops and your heater dies. Don't panic.

Do Not Feed: without a working filter, ammonia will build up fast. Fish can go several days without food; don't add waste to the water.
Insulate Immediately: wrap the entire tank in heavy wool blankets or sleeping bags. Leave a small gap at the top for gas exchange.
The Hot Water Bottle Trick: if the temperature drops below 20°C, fill a plastic bottle with hot (not boiling) tap water, seal it tightly, and float it in the tank. This acts as a temporary radiator.
Have an emergency battery operated aerator to provide oxygen to the tank while the power is out. This will also aid in circulating the water.

Winter Maintenance Checklist

Task	Frequency	Why?
Thermometer Check	Daily	Ensures the heater hasn't stuck on or off.
Water Changes	Weekly	Use a thermometer to ensure replacement water is within 1°C of the tank.
Evaporation Top-up	As needed	Dry winter air increases evaporation; keep the water level high.
Filter Clean	Monthly	Squeeze sponges in old tank water to keep flow optimal.

Stability is Success

The goal of winter-proofing isn't to make the tank "hot"; it's to make it stable. Tropical fish can handle 24°C perfectly well, provided it stays 24°C. It is the jump from 26°C during the day to 20°C at night that triggers diseases like White Spot (Ich).

By checking your equipment now, insulating your glass, and having an emergency plan in place, you’re ensuring that your aquarium remains a stress-free sanctuary for both you and your fish until spring returns.

Need a backup heater or a more accurate thermometer?

Check out the full accessories range at LiveFish to get your setup winter-ready.