An accurate aquarium heater is therefore a necessary accessory to keep your fish comfortable and healthy.
If the tank water is too cold your fish's metabolism slows down and they become susceptible to disease, on the other hand when the water is too warm they become too active and demand more oxygen which may well be in short supply.
The temperature needn't be exactly constant as the range can be quite large over 24 hours in the natural environment, however the general consensus is that variations shouldn't be too great or very quick as this will lead to stress and its associated ill effects.
Although species vary in their preference, it's generally accepted that the optimum temperature range for tropical fish is between 24º – 27ºC (75º – 81ºF) while coldwater species such as the fairground goldfish prefer 15º – 20ºC (60º – 68ºF) in an unheated tank.
Attached to the side of the tank, heaters from TMC, with a temperature range from 20º – 34ºC, Jewel and Fluval vary in power from 50 watts for tanks up to 60 litres to 300 watts if you have a 350 litre aquarium.
Oase manufacture several heaters in the range of 25 - 300 watts and, similar to other heaters, they can be precisely set and will continually monitor and display water temperature.
If you have a biOrb aquarium up to 60 litres, then the biOrb Intelligent Heater would be the best choice. Suitably stylish, the heater is controlled by a micro-processor and offers accuracy and reliability, it can be plugged into the same power pod as the light and pump.
While all these heaters are produced using top quality components and are thoroughly reliable, a temperature gauge such as the biOrb Submersible Digital Thermometer or cheaper alternatives will be an enormous help in keeping an eye on any temperature changes, and this is especially important if by any chance your heater becomes faulty.
So when keeping tropical fish, there's no doubt that a reliable heater is absolutely vital and a temperature gauge very useful, but there are other factors to take into account when maintaining the correct temperature in an aquarium.
For tropical or coldwater fish, the location of your aquarium needs to be taken into consideration. Avoid positioning it in direct sunlight, near a door, window, air conditioning vent or any source of draughts. Radiators are also a problem and aquarium lights will affect water temperature particularly in small aquariums.
Small water changes taking place often are preferable to replacing water wholesale, and it's best to try and match as much as possible the temperature of the fresh water with the existing aquarium water. This is also the case when adding new fish when the temperature inside the bag carrying the fish should be equalized with the tank water.