Since this will be a tropical aquarium, it will require heating.
Fish are poikilotherms, so (in rather crude terms), their environment affects their metabolism. Because fish are not able to regulate their own body temperature, the temperature of the water will affect their enzyme activity, so it is important that an appropriate water temperature, which is sustainable in the long term, is chosen for the fish to live in. This also means that temperature will affect the lifespan and activity level of the fish: for the same fish, a higher water temperature would mean more active fish with shorter life span, while a lower temperature would result in lower level of activity, but with a longer lifespan.
Changes in temperature throughout the year or during a rainy season can also be a breeding trigger for some species of fish. The latter can easily be simulated by large water changes with cool or cold water. Seasons of the year are more difficult, although still possible by setting the heater to a lower temperature in winter and increasing it toward summer, then lowering it again for the winter.
In fishkeeping, fish are usually divided into three groups:
- Fish which live best at water temperatures of 1 – 16 °C, for example, common goldfish
- 15 – 22°C, fish such as fancy goldfish, white cloud mountain minnows and hillstream loaches
- 20 – 30 °C, which include some of the most popular aquarium fish, such as neon tetras and angels
There are, of course, plenty of fish which overlap two (or all) of these groups, or are even outside those temperature ranges altogether. Since there are almost no species of fish, available within the aquarium trade in Europe, which fit into either of the first two categories and a 60 litre aquarium, I have settled on tropical fish.
In an average European household, approximately 1 watt of heater per litre of aquarium water (rounded up, as needed) is enough to keep the water up to temperature when the temperature drops inside the house in winter. Because this is a small aquarium, I will be using the 50 W heater which was included in the set. For aquariums over 100 cm in length, I normally prefer to use more than one heater to make sure that the temperature is the same throughout.
Most heaters have inbuilt thermostats, so it should not matter if the chosen heater gives more than 1 watt per litre of water, but when a heater breaks, it is most often in the “on” state, which means that the heater does not switch off when the water is warm enough. Because of this, I prefer to use appropriately rated heaters, so it is more likely that I will have time to notice the problem, before the fish come to harm.
Internal heaters are usually made out of glass (sometimes with a removable plastic cage around them), polymers and metal. The most common heater are made of glass, but these can be cracked easily, so one has to be careful about letting them cool down properly before taking them out of water and large fish can break them. Polymer heaters are considerably more difficult to break, but are slightly more expensive and difficult to manufacture. Metal heaters are uncommon.
Another common problem with internal heaters is that the numbers on the temperature dial (or a separate scale on the heater itself) do not correspond to the temperature that the heater will be heating to, because these can easily become displaced. This is not a problem, as long as you know how high the displacement is.
On top of the standard internal heaters, one can now buy in-line heaters for external filters, external filter with heaters built into them and undergravel heaters.. but all of these are currently less common and none are suitable for the set-up which I am planning.
In addition to the heater, I will also buy a glass thermometer.