Heating and cooling

Heating and cooling

The right temperature for your aquarium dwellers

Did you know that most tropical waters are “only“ 25 °C, even when the air temperature is above 30 °C? Only large, slow flowing rivers and lakes are an exception because they are less shaded by trees which means they are heated more by the sun. The oceans, of course, are a world of their own.

Thus most fish and plants are most comfortable in your aquarium at 24-26 °C and only a few fish, such as the discus fish prefer temperatures of nearly 30 °C. Many shrimp species on the other hand prefer cooler water and don’t like hot summers at 28 °C water temperature. They do best when small fans are used to cool the water. ( Cooling ).

Aquarium heaters and aquarium coolers

How to heat and cool your aquarium easily and effectively - What temperatures do our aquarium inhabitants have in their natural habitat? What aquarium heaters are there? Rod heater or external heater - which is better? What are the benefits of undergravel heatings in an aquarium? How can you cool the water in summer? We show you all types of heaters, coolers and thermometers and explain the advantages and disadvantages to you


Depending on where you live, your room temperature might be below your desired water temperature. Only in summer and in tropical countries is heating not required. Heater thermostats heat up your water to the pre-set water temperature then switch themselves off. This way your required water temperature is constantly maintained.

The heater thermostat

You can, of course, run your tropical fish aquarium without a heater if your room temperature is warm enough to keep the water CONSTANTLY heated at 24-26 °C. Experience tells us that, without a heater, there will be fluctuations in temperature which are not familiar to your aquarium dwellers in their habitat and which they do not like. An automatic heater thermostat will help you to keep the temperature you need at a constant level. Just set the temperature on a dial on the top of the heater and it will always heat whenever the temperature falls below it. Make sure when inserting the heater that there is a good current around it to prevent heat accumulation, which would lead to it switching itself off instead of heating the aquarium. Select your heater to suit your room temperature. The important factors for the choice of heater power are the size of your aquarium and the temperature difference between room and target water temperature, the so-called ∆T. If you have an external filter connected to your aquarium, you would have the option of integrating an external heater ( JBL PROTEMP e300 or JBL PROTEMP e500 ) into the water return hose of your external filter instead of the "disturbance" of a heating rod INSIDE the aquarium.

For larger aquariums from 250 litres upwards experienced aquarium owners use two heaters instead of one, as they only reach the required water temperature together. In the event of a fault (which is very rare – but as with the safety instructions in a plane, we have to draw your attention towards it) one heater is prevented from causing the unwanted death of the fish.

Please don’t select a too strong heater size to be on the “safe side”! This would lead to the switch on and switch off periods of the heater being very short and switching back and forth too often. This permanent on/off behaviour shortens the service life of any heater!

Substrate heater

It is NOT the task of undergravel heating cables to heat up your aquarium water to the desired temperature but solely to create a water circulation inside the substrate to improve the nutrient supply for the plant roots. Thus a substrate heater is a tool for the care of plants (see Substrate ).

Saving energy

An insulation of your aquarium with a foam underlay and possibly also with a thermal insulation on both sides and the rear pane will help you to save energy costs.


As already mentioned there are aquarium dwellers, such as shrimps which prefer lower water temperatures of 22-23 °C and tolerate high temperatures of 28 °C only for a short time. But a lot of tropical fish species and aquarium plants in particular also feel uncomfortable at high temperatures. Plant growth can even stagnate noticeably because of too high a temperature! JBL provides you with an inexpensive and effective cooling solution which you can easily install in your aquarium:

Fan units (various lengths available) create an air flow at the water surface which leads to an evaporation cooling process (similar to your sensitivity to the cold when you ride a bike). This way you can reduce the water temperature by approx. 4 °C. With a thermostat ( JBL PROTEMP CoolControl ) you can have your fans switched on automatically in case your set temperature is being exceeded.

Temperature control

With the help of a water thermometer you can easily see what’s happening to the temperature in your aquarium. You can choose between various versions and a thermometer which you can stick to the outside of the glass pane: Thermometers & hydrometers .

Measurement and control computer for automatic CO2 addition and pH regulation
from 287,68 €
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JBL Aquarium Thermometer Float
Aquarium thermometer
from 3,00 €
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JBL Aquarium Thermometer Slim
Slim glass thermometer for aquariums
from 7,09 €
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JBL Aquarium Thermometer Digital
Digital aquarium thermometer
from 4,25 €
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JBL Aquarium Thermometer Mini
Aquarium thermometer
from 2,71 €
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JBL Aquarium Thermometer DigiScan
Digital adhering thermometer for aquarium panes
from 16,36 €
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JBL Aquarium Thermometer DigiScan Alarm
Digital adhesive thermometer for aquarium panes with alarm function
from 13,63 €
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External heater for freshwater aquariums from 90 to 300 l
from 50,30 €
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