Platies are an amazing aquarium fish, they work great in all different kinds of aquariums from planted tanks, to communities to breeding setups.
They are great fun for beginners and experts, and are always a pleasure to keep.
However, there seems to be much confusion amongst new fishkeepers as to whether or not these fish can live in cold water.
Can they? What temperature do Platyfish need to be kept at? How can you maintain the right temperature in a Platy tank? And what happens if you keep Platies too warm or too cold?
This and more we will answer below:
Can Platies live in cold water?
The term Platy is often used to describe two different species of fish, these are the southern Platyfish and the Variatus or Variable Platy.
Both of these fish look very similar and are very closely related.
However, they live in slightly different environments, and the Variatus Platy is the one which can be kept in cooler water, being able to live in temperatures anywhere from 15C / 59F to 27C / 80F.
The Southern Platyfish, which is the most common species, is tropical, and needs to be kept at temperatures around 24C / 75F to 28C / 82F.
The fish we will discuss in this article is the Southern Platy (Xiphophorus maculatus) which cannot live in cold water.
Can Platies live in a tank without a heater?
Depending on your situation and location, this answer may change, if you live in a colder region, then it is highly recommended that you install a heater, as it is necessary to keep the Platies alive and well.
If you live in a much warmer climate, and have annual temperatures that stay regularly above 22C / 71F then a heater may not always be necessary.
However, we still recommend having one on hand as a safety measure, especially in the winter time, when the temperature occasionally dips below the recommended safe range.
How long can Platies survive without a heater?
Depending on the severity of the outside ambient temperature difference, this can be a couple hours, to a couple of weeks, it all depends on the situation.
If the outside temperatures are warm, then your Platies may be fine without a heater for as long as the weather stays warm.
In the summertime, your heater may not be needed at all for many days or weeks, if the outside temperature is high enough.
In winter however, this changes, as the outside temperature can quickly cool down the aquarium, below the normal safe range, and your fish may suffer from exposure.
Depending on how cold, they may be safe for a few days, or a few hours, but you do not want to leave your fish exposed to temperatures less than 20C / 68F for any longer than 48 hours.
Why do Platies need a heater?
Platies need a heater because they are true tropical fish, they have adapted over millions of years to live in climates that stay around 24C / 76F annually, and so when kept in captivity, this temperature needs to be replicated.
A heater prevents the tank from dropping below the comfortable temperature range, and having one is a safety measure, ensuring that you are providing the best possible welfare for your fish.
What temperature should a Platy tank be?
Platies are typically most comfortable at temperatures between 24C / 76F and 28C / 82F.
They can be kept at temperatures slightly outside of this range, however, these are the best figures if you want your fish to truly thrive.
From our experience keeping and breeding all different breeds of Platies, we like to keep our fish at 26C / 79F as it seems to be the best spot.
26C allows them to grow at a reasonable rate, digest their food effectively and have the most showy colours, without being overly active or aggressive towards each other.
Types of aquarium heaters for Platy tanks
There are a few different pieces of equipment you can use to maintain the correct temperature in your Platy tank.
The most common heaters are glass aquarium heaters, which come as a rod, containing several metal coils which work similar to a radiator.
They need to be fully submerged in order to work, and are to be placed inside the tank, either in the main display or sump.
Glass heaters are fairly inexpensive, easy to obtain and are highly reliable, which is why they are such a staple piece of equipment in the aquarium trade.
For larger tanks with a sump filter, you may need something a little more powerful, which is where titanium heaters come in.
They are much stronger than a glass heater, and warm up the tank much quicker, which makes them ideal for huge tanks with sumps, as they tend to lose a lot of heat through the level of water movement.
What size heater do I need for a Platy tank?
The size of the heater is all dependent on the size of the tank, and how much water it can hold.
When it comes to internal heating through the use of glass or titanium heaters, we usually suggest getting a unit which has a wattage similar to the amount of litres the tank holds.
For example, a 45 litre Platy tank should have a 50W heater.
A 100 litre tank should have a 100W heater etc.
FAQs about heating Platy tanks
How do you test the water temperature in a Platy tank?
There are a number of ways to test the temperature of your tank, such as thermometer tape, glass thermometers etc.
However, the most efficient and accurate way of testing the temperature is by using a digital thermometer, either a pen, or a submersible display box, which sticks onto the front of the glass with a suction cup.
The submersible thermometers are great, as they are simply battery powered, and give an accurate temperature reading all the time.
Do Platy fry need a heater?
Platy fry absolutely need a heater to survive in their earliest stages, it is very important that they are kept at the appropriate temperature, as their bodily functions and digestion are very fragile at this moment in their lives.
Very tiny fry lack the fat reserves to be able to deal with high temperature fluctuation, so even if the outside temperature is warm, it is recommended to have a heater, just in case a cold spike occurs during the night.
Where does a heater go in a Platy tank?
The type of heater you go with will decide where it should be positioned, for most people who use submersible glass or titanium heaters, the unit will go into the tank, and needs to be fully submerged underwater to work properly.
These types of heaters must stay underwater while powered.
If they become exposed to air while switched on, they will burn out and malfunction, resulting in them bursting or overheating; events which you would want to avoid.
The best spot for a glass heater is along the back of the tank, suction cupped to the glass wall, and placed at a 45 degree angle, preferably where the most water movement is.
As for titanium heaters, the unit is best placed within the sump container, next to the return pump.
If the heater does not have a built-in thermostat, then place the probe at the entry side of the sump tank, so that it detects the cooler water once it enters the sump, and heats it before it leaves.
What happens to Platies if the water is too cold?
Once the water becomes too cold in your Platy tank, the fish will become sluggish, often sitting motionless near the top or bottom of the aquarium, and becoming pale in colour.
They do this because they are cold blooded and depend on the environmental temperature for their own core body temp.
Once the surrounding temperature begins to drop, they will slow down their bodily processes as a way to conserve energy.
Some fish are excellent at coping with this, and can enter a state of hibernation or torpor, being able to lay dormant at sub zero ambient temperatures.
Platies however, are not adapted to do this, and begin suffering from cold related health problems and low immunity below 18C / 64F.
Exposure to temperatures lower than this for a long period of time, will lead to the inability to digest food, dysfunction of normal bodily processes, organ failure and eventual death.
What happens to Platies if the water is too warm?
When the temperature goes above the normal safe range, Your Platies will begin expressing symptoms of stress, often resting in the upper level of the tank, gasping at the surface or rapidly flapping their gills.
They will be especially irritable at high temperatures and will show more frequent signs of aggression and high stress.
Their metabolism will speed up and they will burn off fat significantly faster, meaning they will need feeding more often.
Once the temperature goes above 32C / 90F damage to the fish’s health will occur, and prolonged exposure to these temperatures will result in organ failure and eventual death.
It is very important to maintain a safe temperature range in your aquarium if you want your fish to do well.