What temperature should a fish tank be? Ranges by species

Most tropical freshwater fish tanks should be kept somewhere in 75–80 °F (24–27 °C), and 76–77 °F (24–25 °C) suits the widest mix of community fish. Coldwater fish such as goldfish do best at about 59–73 °F (15–23 °C), usually with no heater, while warm-water species such as discus need about 82–86 °F (28–30 °C). Pick a temperature inside the range of every species in the tank and keep it steady, within a degree or two of the setting day and night.

For a typical tropical community tank, set the heater to 76–77 °F (24–25 °C). Heater makers and care guides give 75–80 °F (24–27 °C) as the usual tropical range, but not every fish is comfortable across all of it, and 76–77 °F falls inside the range of more species in our database than any other setting. Coldwater and warm-water fish are the exceptions, so the right number for your tank is the one that fits every species in it.

Fish are cold-blooded. Their body temperature follows the water, so temperature controls how fast they digest, how much oxygen they use and how well they fight off disease. Getting it right, and keeping it steady, matters more than most new fishkeepers expect.

Quick answer by type of tank

Type of tank	Temperature	Heater needed?	Typical fish
Tropical community	75–80 °F (24–27 °C)	Yes	Tetras, rasboras, corydoras, livebearers, gouramis
Warm-water specialists	80–86 °F (27–30 °C); discus 82 °F (28 °C) or more	Yes	Discus, German blue rams, clown loaches, zebra plecos
Temperate (“room temperature”)	64–72 °F (18–22 °C)	Only if the room gets colder than the fish’s range	White cloud mountain minnows, zebra danios, rosy barbs
Coldwater	59–73 °F (15–23 °C)	No, in a heated home	Common and fancy goldfish

Why the right temperature matters

Too warm. A fish’s metabolism speeds up as the water warms, so it needs more oxygen at exactly the moment the water can hold less. University of Florida extension figures show that fully saturated water holds about 11.9 mg/L of oxygen at 45 °F (7 °C) but only 7.4 mg/L at 90 °F (32 °C). Fish kept permanently warmer than they need can also live shorter lives; white cloud mountain minnows are a known example.

Too cold. Tropical fish slow down, lose their appetite, hide with clamped fins and become more prone to disease. University of Florida fish health specialists note that ich (white spot) outbreaks often appear when the water temperature is changing quickly, and cooler water weakens fish immune defenses.

Swinging. Sudden changes stress fish even when both temperatures are inside their range. This is one reason small bowls are a poor home: a little water heats and cools quickly with the room.

Temperature ranges for popular aquarium fish

These ranges come from FishFits’ species database, where each species page lists its sources. Treat them as comfortable ranges, and aim for the middle rather than the edge.

Species	°F	°C	Notes
Common goldfish	59–72	15–22	Coldwater; no heater
White cloud mountain minnow	61–72	16–22	Coldwater; no heater in most homes
Fancy goldfish	64–73	18–23	Coldwater; no heater in most homes
Rosy barb	64–75	18–24	Happy in cooler, unheated tanks
Zebra danio	64–77	18–25	Very tolerant; tropical or temperate
Celestial pearl danio	68–77	20–25	Prefers the cooler side of tropical
Platy	68–79	20–26
Neon tetra	70–77	21–25	Cooler than most tetras
Bronze corydoras	70–79	21–26
Guppy	72–81	22–27
Harlequin rasbora	72–81	22–27
Tiger barb	72–81	22–27
Bristlenose pleco	72–79	22–26
Cherry barb	73–81	23–27
Cardinal tetra	73–82	23–28	Handles warmer water than neons
Sterbai corydoras	73–82	23–28	The usual cory for warm tanks
Molly	75–81	24–27
Kuhli loach	75–81	24–27
Dwarf gourami	75–82	24–28
Rummy-nose tetra	75–82	24–28
Betta	75–82	24–28	Around 78–80 °F suits most
Angelfish	75–84	24–29
Clown loach	77–86	25–30	Warm-water fish; grows large
Zebra pleco	79–86	26–30	Warm, fast-flowing water
German blue ram	81–86	27–30	Too warm for most community fish
Discus	82–86	28–30	Needs warm, steady water

Notice how far apart some popular fish are. A neon tetra tops out at 77 °F (25 °C), the bottom of a clown loach’s range, while a white cloud mountain minnow and a cardinal tetra share no temperature at all.

How to choose one temperature for a mixed tank

List every species in the tank, or that you plan to add, including shrimp and snails.
Write down each one’s range from the table above or its species page.
Find the overlap: from the highest of the minimums to the lowest of the maximums.
Set the heater near the middle of that overlap, so normal swings stay inside it.
If there is no overlap, change the plan rather than splitting the difference. If the overlap is narrower than about 3 °F (1.5 °C), there is little room for a hot day or a heater fault, so think twice.

Worked example. Neon tetras (70–77 °F), bronze corydoras (70–79 °F) and harlequin rasboras (72–81 °F) overlap at 72–77 °F (22–25 °C), so 74–75 °F is a good setting. Add a dwarf gourami (75–82 °F) and the window shrinks to 75–77 °F (24–25 °C). A setting of 76 °F works, but the margin is thin, so watch the thermometer closely in summer or choose a tank mate with a closer range.

You don’t have to do this by hand. The compatibility checker shows the shared temperature for any group of species, and the stocking calculator flags fish that can’t share a temperature as you build a stocking list.

Coldwater and room-temperature fish

Goldfish are coldwater fish. Our species data puts common goldfish at about 59–72 °F (15–22 °C) and fancy goldfish at about 64–73 °F (18–23 °C). Common goldfish in particular tolerate colder water than that, and some care guides go as low as 50 °F (10 °C), but the bands above are where they do best. In a home with heating and air conditioning they rarely need a heater. Keeping them warmer speeds up their metabolism and waste output, and it rules out sharing a tank with tropical fish.

Temperate fish such as white cloud mountain minnows (61–72 °F / 16–22 °C), rosy barbs and zebra danios sit between the two groups. They often do well unheated, but “room temperature” is not one number: a tank near an outside wall can drop several degrees on a winter night. Put a thermometer in for a week before deciding. If the water falls below the bottom of the fish’s range, a heater set low (around 68 °F / 20 °C, the lowest setting on many adjustable heaters) works as a safety floor rather than a warmer.

Fish that need warmer water

A few popular fish want more heat than a standard community tank:

Discus: 82–86 °F (28–30 °C), held steady. Many discus-only tanks run at 85–86 °F (29–30 °C).
German blue rams: 81–86 °F (27–30 °C). They need 81 °F (27 °C) or warmer, which is too warm for many community fish.
Clown loaches and zebra plecos: 77–86 °F (25–30 °C) and 79–86 °F (26–30 °C) in our data, so both are happy in a warm tank.

Tank mates for these fish must handle the heat. Cardinal tetras and sterbai corydoras are the usual small companions for discus because they cope with warmer water than neon tetras and most other corydoras. Even so, their ranges reach only 82 °F (28 °C) in our data, the bottom of the discus range, so a mixed tank like that belongs near 82 °F rather than at 85–86 °F. Warm tanks also hold less oxygen, so keep the water surface moving with the filter outflow or an air stone.

How to size and set up a heater

Heater size depends on how much warmer the tank must be than the coldest the room gets. Aquarium Co-Op’s rule of thumb is 5 watts per gallon (1.3 W per litre) for a tank with a lid that needs to be up to 10 °F (5–6 °C) warmer than the room. Heater makers’ charts for mid-size and large tanks come out lower, closer to 3 watts per gallon. Small tanks lose heat faster for their size, and cold rooms and open tops need more.

Tank	Heater size (room up to 10 °F / 5–6 °C cooler, lid on)
5 gallons (19 L)	25 W
10 gallons (38 L)	50 W
20 gallons (76 L)	50–100 W
29 gallons (110 L)	75–150 W
40 gallons (151 L)	100–200 W
55 gallons (208 L)	150–300 W, split over two heaters
75 gallons (284 L)	200–400 W, split over two heaters

The lower figure is what our calculator gives, and the higher one follows the 5 W per gallon rule; most makers’ charts fall between the two. Lean toward the higher figure for a cool room, a drafty spot or an open top, and plan for more if the room drops below about 65 °F (18 °C) in winter. For a figure based on your own tank, room and target temperature, use the heater size calculator. Then set it up like this:

Mount the heater near the filter outflow so warmed water spreads around the tank. Tube heaters are often angled at about 45°, but follow the maker’s instructions on which way up it can go and how deep it must sit.
Put a thermometer at the opposite end of the tank, away from the heater.
Let the heater sit in the water for as long as its instructions say (often 20–30 minutes) before plugging it in, so the glass can adjust to the water temperature.
Set the dial, wait 24 hours, then read the thermometer and adjust. Dial markings can be off by a degree or more, so trust the thermometer.
On tanks over about 50 gallons (190 L), use two smaller heaters instead of one big one. If one fails, the other keeps the tank from crashing, and if one sticks on, it is less likely to overheat the tank on its own.

Avoid putting a heater much bigger than needed in a small tank. If its thermostat sticks in the on position, a large heater can overheat a few gallons of water within hours. An external heater controller with its own probe adds a safety cut-off.

How to keep the temperature stable

Place the tank well. Keep it away from sunny windows, radiators, air-conditioning vents and outside doors. Direct sun can push the water dangerously high.
Use a lid. It holds in heat and cuts evaporation, which cools the tank.
Check the thermometer every day. Heaters and thermostats do fail, and a glance at feeding time catches problems early.
Match water-change water. Get new water within about 2 °F (1 °C) of the tank before you pour it in, and check it with a thermometer, not your hand. The water changes guide covers the full routine.
Unplug the heater before draining. A heater left running in air can overheat and crack when the water returns.
Acclimate new fish. Float the sealed bag for about 15 minutes so its water reaches tank temperature, as described in the fish acclimation guide.
Go bigger if you can. A large volume of water changes temperature far more slowly than a small one.

How to cool an overheating tank in summer

Most of the community fish in the table above top out between 77 and 82 °F (25–28 °C). If the water climbs above the top of your fishes’ range and keeps rising, or the fish are gasping at the surface or breathing fast, act now:

Unplug the heater or turn it to its lowest setting.
Turn off the aquarium light and close blinds or curtains on that side of the room.
Add surface movement. Lower the water level slightly so the filter splashes, or add an air stone. Warm water holds less oxygen, and this is the most important step for the fish.
Open the lid and point a fan across the water. Evaporation pulls heat out of the tank and can lower it by a few degrees. Leave a cover over part of the top if you keep jumpers, and top up the lost water with dechlorinated water.
Float a sealed bottle of frozen water. Swap it for a fresh one as it thaws. Never drop ice cubes made from untreated tap water straight into the tank.
Feed lightly. Digestion raises oxygen demand, so skip a meal or feed half the usual amount on very hot days.
Cool it slowly. Aim to bring the water down over several hours. A big change of cold water swaps one shock for another; if you change water, use water only a few degrees cooler than the tank.

If fish are still gasping once the water is back in range, test for ammonia and nitrite, and contact an aquatic vet if they don’t recover. If the room regularly gets hotter than your fish can handle, the long-term fixes are air conditioning in that room or an aquarium chiller.

If the tank gets too cold or the power goes out

Signs of a chilled tank are fish resting on the bottom, clamped fins, slow movement and refused food. Check the heater first: is it plugged in, and does its indicator light come on? Raise the temperature back to normal gradually, over several hours rather than all at once. Watch the fish closely for the next two weeks, because ich often breaks out after a sudden temperature change. If white spots appear, treat as the ich guide describes and follow the medication label exactly. If fish keep getting sick or dying, contact an aquatic vet.

During a power cut, keep the lid on and wrap the tank in blankets, towels or a sleeping bag to hold in heat. Don’t feed, and run a battery air pump if you have one. If the cut lasts many hours, float sealed bottles of warm (not hot) water and refill them as they cool.

Common mistakes

Trusting the heater dial instead of a separate thermometer.
Mixing coldwater and tropical fish, such as goldfish with tetras or white clouds with cardinals.
Setting the temperature at the edge of a range, so the first hot day or cold night pushes the fish outside it.
Using a heater too small for a cold room, so it runs nonstop and still can’t reach the set point.
Doing large water changes with cold tap water in winter.
Setting everything to 82 °F (28 °C) “to be safe”, which is too warm for many popular community fish.
Ignoring summer. A tank in a sunny room or without air conditioning can overheat even with the heater switched off.

Gear mentioned in this guide

Adjustable aquarium heater (opens Amazon in a new tab)Use the heater calculator for the right wattage for your tank and room. How to choose
Aquarium thermometer (opens Amazon in a new tab)Check it daily: heaters can fail stuck on or off. How to choose
Clip-on cooling fan (opens Amazon in a new tab)Lowers the water temperature in summer by evaporation. How to choose

Product links go to Amazon search results. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. Disclosure.

Frequently asked questions

Is 80 °F too hot for a fish tank?

Not for most tropical fish. 80 °F (27 °C) is inside the range of guppies, cardinal tetras, rummy-nose tetras, dwarf gouramis and many others, but it is too warm for neon tetras, panda corydoras, white cloud mountain minnows and goldfish, which top out at 77 °F (25 °C) or lower.

Do I need a heater for my fish tank?

For tropical fish, almost always, because few rooms stay at 75 °F (24 °C) or warmer day and night all year. Goldfish and temperate fish such as white cloud mountain minnows can usually live without one in a heated home.

Should I turn the aquarium heater off at night?

No. Leave it plugged in and let its thermostat decide when to heat. A small dip of a degree or two overnight is harmless, but switching the heater off lets a tank in a cool room fall much further.

Can goldfish and tropical fish live together?

No. Goldfish do best at about 59–73 °F (15–23 °C), while most tropical fish need 75 °F (24 °C) or warmer, so one group always ends up outside its comfortable range. Goldfish also produce far more waste than most small tropical fish.

What temperature should a betta tank be?

Keep a betta between 75 and 82 °F (24–28 °C), ideally around 78–80 °F (26–27 °C), with a small adjustable heater. Many US homes sit at about 67–69 °F (19–21 °C), and at that temperature an unheated betta turns sluggish and is more likely to get sick.