Best Water Temperature for Fancy Goldfish: Do They Need a Heater?

Fancy goldfish are not all the same when it comes to temperature. Most care sheets say to keep goldfish cool, but fancy goldfish raised on Thai farms live in warm water from the day they hatch. Here is what we recommend, why it works, and how to keep the temperature steady.

The Short Answer

For Thai-bred fancy goldfish such as Ranchu, Lionchu, and Oranda, we recommend 78 to 80°F with strong aeration. The most important rule is to keep the temperature stable. A tank that swings 5 to 10 degrees in a day is harder on your fish than a tank that stays at one steady number.

Why Thai-Bred Goldfish Like Warmer Water

Goldfish farms in Thailand are warm all year. Our fish grow up at those temperatures, so their bodies are used to it. When a fish moves from warm farm water into a cool tank, it has to adjust to a big change, and that adds stress right after shipping.

If you keep a goldfish from a cooler source, such as a pond-raised or domestic fish, a lower temperature may suit it better. Ask your seller where the fish was raised.

Do Fancy Goldfish Need a Heater?

If your room stays between 78 and 80°F all year, you may not need one. Most homes are cooler than that, especially at night and in winter. An adjustable heater with a built in thermostat is the easy way to keep the water steady.

• Size the heater to the tank. A common rule is about 3 to 5 watts per gallon.
• Use a heater guard. Slow swimmers like Ranchu can get burned on bare heaters.
• Add a separate thermometer. Do not trust the dial on the heater alone.

How to Set the Temperature for New Fish

When your fish arrive, follow the slow steps in our goldfish acclimation guide. Match the tank to the bag water first. If you need to change the temperature, move it 1 to 2 degrees per day, not all at once.

Warm Water Means a Little More Work

Warmer water speeds up a fish's metabolism. That is good for growth and color, but it also means:

• Less oxygen in the water. Run strong aeration with an air pump and air stones.
• More waste. Fish eat more and make more waste, so keep up with water changes. See how to do a water change without stressing fish.
• Faster bacteria growth. Test ammonia and nitrite often. Our tank cycling guide explains why.

What to Do in a Summer Heat Wave

If your tank rises above 82°F, take these steps:

• Turn off the tank light and run a fan across the water surface.
• Keep air stones running and add one if you can.
• Cool the room if possible.
• Do not drop the water temperature fast with ice. Slow changes are safer.

We also recommend keeping aquarium salt in the water. See our aquarium salt guide for goldfish.

Frequently Asked Questions

What is the best temperature for fancy goldfish?

For Thai-bred fancy goldfish, we recommend 78 to 80°F. Keep it steady.

Can goldfish live in 78 to 80°F water?

Yes. Thai-bred fancy goldfish are used to warm water. Goldfish raised in cooler places may prefer a lower range.

What temperature is too hot?

Water above the low 80s for long periods holds less oxygen and stresses fish. Add aeration and cool the room.

What temperature is too cold?

Cool water slows digestion and can weaken fish that came from a warm farm. If the tank drops well below 78°F, fish may eat less and are more likely to get sick.

Do I need an air stone?

Yes. Strong aeration matters more in warm water, because warm water holds less oxygen.

Shop Fancy Goldfish From San Diego

Browse our Ranchu, Lionchu, and Thai Oranda. Read our live fish shipping guide before you order.