Guppies are one of the most commonly sold aquarium fish worldwide, they are easy to keep and to breed, they are an ideal beginner fish, and fit into a wide range of set ups.
But do you need a heater for these fish, what temperature should Guppies be kept at, and what methods of maintaining the temperature can you adopt?
Read this guide to find out:
Can Guppies live in cold water?
There are actually a handful of different species of Guppies out there, and some of these can live at slightly different temperatures than others.
However, the species of Guppy we are talking about today are the most common species in the aquarium trade; Fancy Guppies (Poecilia reticulata) which are indeed tropical fish.
Fancy Guppies originate from the more northern areas of South America, close to the equator, where the annual temperature stays very warm, seldom dipping below 15C / 59F outside of a few cold spikes during winter.
For this reason, Guppies prefer to live at your standard tropical fish temperatures, and do not do well when kept in cold water.
This is the same for every breed and strain of Fancy Guppy, as they are all the same species.
Can Guppies live in a tank without a heater?
The answer to this question will vary depending on your situation.
For some people, their home already sits at around 24C / 75F and so a heater is not always necessary.
However we would still recommend one as a safety measure for when times do get cold, and the room temperature drops below the norm.
For others who live in temperate or cold areas, a heater is nearly always necessary to keep the tank at tropical levels throughout the year, and to keep the fish in healthy condition.
How long can Guppies survive without a heater?
Depending on the surrounding temperature, this answer will differ greatly.
In the height of summer when it is hot all day and warm in the evenings, Guppies can live many weeks without a heater.
Many people actually switch their heaters off in summer to save electricity, as the tank will remain warm from the ambient temperature.
However, if it is cold outside, the tank temperature will dip, and the Guppies will experience temperatures outside of their normal range.
It is not recommended to expose your guppies to temperatures below 20C / 68F for any longer than 48 hours, by this time, your fish will experience high stress and will be vulnerable to health problems.
The colder the temperature, the less time the fish should be exposed, for example 14C / 57F is very cold for Guppies, and they should not be allowed to stay at this temperature for very long, the fish will immediately show signs of lethargy and stress.
Any longer than 2 – 3 hours in temperatures below 14C / 57F and they will likely begin expressing health problems.
Why do Guppies need a heater?
Guppies require a heater because having one allows you to better control the temperature of the tank, and better simulate the natural environment which Guppies are adapted to live in.
Guppies are tropical fish, and have evolved to live in temperatures that regularly stay above 22C / 72F.
They are not well adapted to living in a cold environment, and so it’s our job when keeping them in captivity, to make their habitat suitable, to give them the best possible welfare.
What temperature should a Guppy tank be?
Guppies prefer to live at temperatures that sit anywhere between 24C / 76F to 27C / 80F.
This is the safe range which Guppies should be kept at.
While they can be kept outside of this range in some cases, these are the temperatures they seem to do best in.
Depending on whether you keep them warmer or cooler can also influence their lifestyle to a degree.
If you keep your Guppies at 24C / 76F, their metabolism will be slower, they will grow slower, but will live longer lives.
If kept at 27C / 80F they will grow quicker, eat more and will live shorter lives, as is the case with most tropical fish.
After our years of experience in keeping and breeding all different types and strains of Fancy Guppies, 25C / 77F seems to be the sweet spot for them.
Types of aquarium heaters for Guppy tanks
There are all different kinds of heaters you can use on a Guppy tank, it all depends on your situation, and what you believe would work best for your setup.
For many, a small glass aquarium heater is enough to keep their tank warm.
For those with huge tanks that have a sump, a titanium heater may be more effective.
For others, heating the room itself is much more cost effective and easier to manage.
Glass heaters are great as they are simple to use, widely available, and are highly adaptable, being usable in most aquarium setups.
All you need is to place it in the tank, fully submerged at a 45 degree angle, set it to the correct temperature you want, and plug it into an electrical outlet.
Glass heaters come in all different sizes too, so they are suitable for 5 gallon nano tanks all the way up to huge 200+ gallon tanks.
Titanium heaters are best used for larger tanks, especially those which have a sump filter, as they are very powerful pieces of equipment.
They are best sat along the bottom of the sump tank or stuck to the back wall of the tank, close to the return pump.
They are excellent at heating larger tanks, but aren’t really necessary for smaller setups.
What size heater do I need for a Guppy tank?
The size of heater is determined by the amount of water your tank holds, as a typical rule, we usually suggest for glass heaters to have a wattage number that correlates with the amount of litres the tank holds.
In short you want the Wattage to be as close to the number of litres as you can.
You won’t always find something that exactly matches up, but as long as the wattage is close to the literage, then it should work fine.
Sometimes it works best to go slightly over with the wattage if you are faced with an uneven number.
For example, say you have a 10 gallon Guppy tank, (45 litres in imperial gallons), you would want to use a 50W heater.
If you have a 90 litre tank, a 100W heater would work best, and so on.
When it comes to very large tanks that hold over 300 litres, you may want to use a titanium heater, or use multiple glass heaters to ensure that the tank stays warm.
FAQs about heating Guppy tanks
How do you test the water temperature in an Guppy tank?
The best way to find out the water temperature in your tank is through the use of a digital thermometer.
Digital thermometers are the most accurate and quickest way of finding the specific temperature of the water.
There are all different types of digital thermometers, but the digital pens designed for water testing work best.
TDS metres often have a thermometer built into them, and are what we most prefer to use when judging the temperature of our aquariums.
These pens are very easy to use, they are battery powered, easily transportable, and work by dipping the probe into the water for a few seconds, and looking at the heads up display to be given the temperature.
Other tools you may use include thermometer tape; which is stuck on the outside of the tank, and changes a blue or green colour over the right temperature to signify how warm the tank is.
Or a classic glass thermometer, which sits in the water all the time.
Different glass thermometers use different substances inside, many use mercury, which changes shape depending on the temperature, and will rise or fall as the degrees change.
Do Guppy fry need a heater?
Young Guppy Fry definitely need a heater, and should be kept warm at all times.
It is especially important that the fry stay warm, as they are too small to have the fat reserves that can cope with low temperatures.
You should always keep the fry at around 25C / 77F to promote healthy growth.
Where does a heater go in an Guppy tank?
Depending on the type of setup you have, the heater can go in a number of different places.
For most people using a standard glass heater, it will simply attach to the back of the tank with a pair of suction cups, best kept at a 45 degree angle for the highest effectiveness.
For those with a sump filter, the heater is best placed in the sump tank, where there is the most water movement.
Placing the heater next to the return pump is the best place, as it will reheat the water before it gets flushed back into the main display tank.
In a sump filter, a glass or titanium heater may be used, and can be stuck onto the back of the glass, or more preferably, placed along the bottom of the tank, so that it releases heat more effectively.
For a titanium heater without a built-in thermostat, place the thermostat probe at the entry side of the sump, so that the water in the display tank can be more accurately determined and heated up accordingly.
What happens to Guppies if the water is too cold?
When a Guppy enters temperatures below their normal comfortable range, you will notice that they immediately become sluggish and grow pale in colour.
Their bodily processes will slow down as they try to preserve energy, and they will sit motionless in the water.
A prolonged exposure to temperatures below 18C / 64F will cause low immunity, discomfort, sluggishness, inability to properly digest food, eventual organ failure and death.
What happens to Guppies if the water is too warm?
When kept in temperatures that are too high, Guppies often become very active, very irritable and uncomfortable, exhibiting more aggressive behaviours more frequently, like fin nipping and bashing each other with their tails.
They will also feel the need to eat more and will lose weight very quickly, as their metabolic rate speeds up.
You may end up feeding your Guppies much more frequently at higher temperatures to keep up with their voracious appetite.
Their lifespans will also be much shorter if kept at higher temperatures, and they will grow, breed and die off much faster than normal.
If kept extremely warm, outside the normal range, well above 32C / 90F they will very quickly develop health problems, and will be seen gasping at the top of the tank for air, rapidly flapping their gills, in a highly stressed state.
Being exposed to high temperatures for too long will result in organ failure and death, so it is important that in the height of summer, some effort is made to prevent the temperature from going over 32C / 90F for too long, and that the tank temperature is kept within the safe range.