All fish, whether tropical or not, have an ideal temperature range in which they will thrive well. In the majority of cases, they do not need a precise and unmoving aquarium temperature.
Tropical fish tank water should feel slightly lukewarm to touch. It will feel slightly cooler when it’s warm outside of the tank, and slightly warmer when it’s cold outside of the tank. Always use a thermometer to check the water temperature is correct.
Do Tropical Fish Need Warm Water?
Maintaining your aquarium within a particular temperature range is crucial to ensure that your fish stay healthy and happy.
First, we need to know a little about fish in their natural habitats.
When fish are in their natural habitat, the water temperature is not constant, and fluctuates quite a bit. Some days it can be sunny, whilst other days it is cloudy, and therefore cooler.
As you move further away from the equator, there will also be more defined seasonal changes.
The water on and just under the surface tends to be a lot warmer than a few meters below, due to the heat from the sun.
There is a major difference between tropical fish in their natural habitat, and tropical fish in an aquarium, in relation to water temperature.
Fish in their natural habitat will move to a more desirable place if they are not comfortable with the temperature. Temperature variations tend to happen slowly and steadily in nature due to the vast amounts of water involved. This means that the fish have enough time to adapt to or move away from a particular area if they feel uncomfortable.
This, however, is not the case for fish in an aquarium.
The temperature in an aquarium tends to be constant throughout. The fish don’t have the choice to be able to move to a more comfortable area if needed.
The temperature within a fish tank can change swiftly as well, due to it being a much smaller body of water. This means the fish do not have the time to be able to adapt to any temperature change.
How Hot is Too Hot for Tropical Fish?
Fish are cold blooded animals. This generally means that they cannot control their internal body temperature but depend on their environment to regulate their metabolism, activity levels, and their body temperature.
Tropical fish are generally most comfortable in a temperature range between 75-80 degrees Fahrenheit. Depending on the species, some fish are more comfortable in the lower part of this range, whilst others prefer the higher part of the range.
There are some species of fish, for example, Danios, who are very hardy and will be fine in water even a little cooler than that.
If the temperature creeps up to and over 83 degrees Fahrenheit for a prolonged period of time, this will start to affect the health and stress levels of your tropical fish.
As the water gets warmer, the oxygen levels start to dwindle. This is mostly due to the fact that when the temperature is too warm, the breathing and metabolism rate of your fish will increase, so they will use more oxygen. This will make them become more lively, which in turn will make them need more oxygen, and so on…
The warmer temperature will also start to kill off your good bacteria within the tank which will potentially start an ammonia spike, which can be fatal to your fish.
Warmer water will make your fish more vulnerable to disease, and in the most severe cases, they could suffocate or suffer catastrophic organ failure.
Should a Fish Tank Heater be Hot to Touch?
A fish tank heater uses electricity to heat the water in your tank. The electrical part that heats the water is encased in a glass tube, then covered with a plastic casing. This casing protects the fish from burning themselves on the glass tube. The glass tube keeps the electricity part away from the water, as the two definitely do not mix!
Your water heater should not be too hot to touch, due to the plastic casing that surrounds it that protects the fish. If it is too hot to touch, contact the manufacturer for advice. If it is too hot for you to touch, it will be extremely dangerous for your fish.
I have found this really interesting video made by Aquarium Co-op about aquarium heaters. They have some really good tips on how to prolong the life of your fish tank heater.
If you haven’t already heard of these guys, they are very informative. I listen to their podcast a lot.
What to do if the Fish Tank Water Feels Cold.
As with if your tank water gets too hot, if your tank water gets too cold, this can also be a problem for your fish.
If your tank water feels cold, check that your heater is working correctly. Use a thermometer to confirm that the temperature displayed on your heater is correct.
If you heater is working, don’t panic. If it is a hot day and you put your hand in the water, it is going to feel colder, as the temperature in the room is warmer.
Where have your hands been just before you touched the water? If, like me, you wash your hands before putting them in the water, if you have used hot water, the fish tank water is going to feel cooler as they temperature of your hands will have risen whilst washing them.
If, after checking your heater, and then double checking with your thermometer, you realise that your heater isn’t working properly, you will need to take action.
Double check that the plug hasn’t somehow come out of the socket at all, and that the heater is switched on.
If it is definitely broken, switch it off and take it out of the water. Don’t try and switch it on out of the water while it is still wet or you could end up broken as well.
Your main concern is to not let the temperature of your water drop too low that it affects the health of your fish. When the water is too cold, they will stop moving around.
If you don’t have a spare heater, get a new one ordered or bought immediately.
Try and keep the tank warm by wrapping it in bubble wrap or towels. Bubble wrap is better because you will still be able to see the fish.
If you have a large tank that is understocked, it may be better for you to move them to something smaller, where it is easier to control the water temperature, whether that be a quarantine tank (if you have one), or a bucket.
Don’t forget that when your new heater arrives, it can take a day or 2 to get the tank water to the correct temperature, so you may need to keep the tank still covered at first.
Tropical fish water in your tank should be within a set range. As long as it is within that range, it is perfect for your fish. It may not feel warm to us humans, but this can be due to a number of factors, such as the temperature in the room the tank is in.
Always use a thermometer to double check the water temperature if you are ever in doubt.
It is better to be safe than sorry.