How to keep a fish tank warm if the power goes out

When power cuts happen your aquarium can quickly suffer with drops in temperature and a lack of filtration so here’s what to do if you find yourself without power.

1. Insulate the tank. If your tank has a lid, make sure it’s on. If there’s no lid, make one out of cardboard. Then, cover the tank on all sides with blankets, towels, polystyrene or cardboard. This will help the tank stop losing heat. Make sure to cover the tank entirely to allow oxygen in, particularly if you have surface breathing fish. It’s helpful to have space blankets on hand for this step.
2. Use hand warmers. The best heatpacks to have on hand are the 60 hour or 72 hour kind that are typically used for shipping fish. Place a few around the tank and loosely cover with the blanket. You may want to consider rechargeable ones (be careful not to get them wet) or reusable gel packs if power cuts are expected to be frequent.
3. Use hot water if you can still heat it. A gas hob or camping stove will allow you to heat water. Be very careful to heat it only a few degrees above the desired temperature, add warmed water slowly and monitor the temperature closely. You can also put hot water inside a bottle and float it in your aquarium. Don’t forget to dechlorinate it just in case of leaks.
4. If you have no access to heat, 100g of calcium chloride added to approx 475ml of water inside a water bottle will react and generate heat. Make sure not to leave any residue on the outside of the bottle and float it in your aquarium. Make sure to monitor the temperature for this one.
5. Candles can be used as a heat source if none of the above is available but it’s not recommended because of the increased fire risk but if you’re able to watch the tank and use them safely they can be effective. Stick to tealights and if possible use ceramic / terracotta holders which will retain and slowly release heat. Place a few around the tank (away from the glass) and ensure there is no risk of the flames meeting any furnishings. Do not use candles if your tank is covered in blankets.
6. If your power will be out for some time a battery powered air pump may be necessary to oxygenate the water.