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Lowering the water temperature in aquarium

On hot days many of us are looking at the aquariums and envy our fish for being able to sit in water all the time. Instead of sitting at work or in an overheated living room, who wouldn’t want to swim in a pool? Is it really that “fun” for the fish? But is lowering the water temperature in aquarium necessary on hot days?

Higher temperature means less oxygen in the water

Remember that the greatest amount of dissolved oxygen is observed in rushing and cold mountain streams. As the temperature increases, the oxygen level in the water decreases. This problem affects any environment, from a pond to a home aquarium. Not all of us can afford air conditioning in our home or apartment, and on warm summer days, indoor temperatures often exceed 30⁰C.

Remember that the greatest amount of dissolved oxygen is observed in rushing and cold mountain streams. As the temperature increases, the oxygen level in the water decreases.

Most fish are adapted to live in an environment with a temperature of 24 – 26⁰C and this is considered the “standard” temperature in aquaristics. Some species prefer cooler waters, e.g. cardinalfish, Notropis chrosomus (18 – 22⁰C), others, e.g. discus or loaches, prefer warmer waters (26 – 30⁰C). Fish can adapt to some extent to temperatures different from those prevailing for decades in their natural environment, but this usually affects their behaviour, feeding patterns and life expectancy.

The story of one axolotl

A few years ago, a lady came into my shop. She noticed the axolotls in the aquarium and listened with fascination about their evolution and body structure. After a few days and completing the aquarium, she returned to purchase a new pet. Axolotls have external gills and live in relatively cool oxygen-rich waters where they do not need gill covers to move oxygenated water through their respiratory system. The problem occurred in the summer when the water temperature rose due to hot weather. Lowering the aquarium water temperature was necessary. What did our creative client do? She purchased a large wine cooler that her friend, an appliance repair technician, customized to operate at a constant 18⁰C and installed LED lighting. From that moment on, the tank, although smaller, but two-level (there was a small sump connected to the aquarium at the bottom), was placed in a lighted cooler. Weird? Unusual? And on top of that… expensive? Maybe, but it worked. In summer, the axolotl called Franek looks at his owner through a double pane window.

Specific heat of water

Without a doubt, water is a truly amazing chemical. We could talk for hours about hydrogen bond formation, dipole structure, great solvent properties, etc. Unfortunately (from our point of view), it also has a very large specific heat, which is the heat (energy) needed to change one unit of temperature by one unit of mass. To sum up, if we want to raise or lower the water temperature by 1⁰C we have to put a lot of energy into it. There are many ways to lower the water temperature. I’ll cover the most popular ones, from basic to advanced.

Ways of lowering aquarium water temperature

  • Shade the area around the aquarium – if the tank is in contact with sunlight or the room, where it is located in, is strongly lit during the day, cover the windows with blinds or shades.
  • Open the cover of the tank a bit – water evaporating gives up heat to the environment. Many people ignore this fact, fearing large losses of water associated with it, but nature in this way tries to regulate the temperature and it is worth allowing her to do so.
  • Shorter lightning time – even the newest types of LED lighting generate heat. On hot days it is advisable to shorten the time of lighting the tank.
  • Increase the distance between the water surface and the light source as lighting, by generating heat, affects the water temperature. Hang the lamp on the ceiling and adjust its distance from the water surface, this way you can also lower the temperature in the tank. Having an aquarium cover is not a problem either – just put a small square of 1 cm or similar material on the aquarium to “lift” the whole cover.
  • Use a fan – “blowing” warm air which is formed between the light and the water surface allows, according to various estimates, to reduce the temperature by 1 – 2⁰C. This is a lot! For this purpose we can use a room fan, assemble a set using computer fans or buy fan sets dedicated to use in aquaristics. They have an undeniable advantage – you can direct the airflow at different angles and securely mount them on the edge of the tank.
  • Ice – water frozen in a bottle or fish bag, dropped into the tank will help reduce the temperature. It takes a lot of time, but cyclic replacement of containers brings very good results and allows to reduce the temperature by 3 – 4⁰C.
  • Aquarium chiller – the most advanced method of cooling aquarium water. The water, flowing in a spiral through the device, is cooled down to the temperature set by the aquarist. A cooler is not cheap, but in case of large tanks (freshwater or marine) and/or valuable specimens swimming in the aquarium, it proves to be a very useful piece of equipment.

What else do people recommend and what isn’t quite worth doing?

Putting ice cubes into the tank – the method might be effective in case of small, a dozen or so liter aquariums, when they are prepared with RO/RODi water it allows to replenish the evaporated part of the liquid. However, there is never enough evaporation in a small area to just make up the shortfall – we always encounter excess water, which involves water changes. I will tell you more later on…

Try much more frequent and intensive water changes – many people use tap water for this purpose, usually at least 10⁰C cooler than our surroundings. It would seem to be a perfect solution but water for aquarium purposes must be treated. In addition, cooling down the tank too quickly can lower the immunity of the fish and thus cause diseases. Imagine jumping between icy and hot showers – this is how fish feel when temperatures suddenly jump.

Remember that summer is a time when there is less drinking water in the nation’s water supply. This can affect its quality and parameters. The water that goes into our taps must meet stringent Ministry of Health standards, but what is acceptable to humans (often in broad ranges) can weaken a small home ecosystem.

Take care of the oxygen in the water

Each method of lowering the water temperature in aquarium has its pros and cons, and any responsible aquarist will choose the method that suits him or her best. Do not forget to oxygenate the water more intensively, and during holidays provide the fish with supervision of an experienced person and install an additional, even smaller filter. Overfeeding leads to an overproduction of metabolites, and the bacteria in the water need a lot of oxygen to process these metabolites, which are already in high demand in the tank.

Michał Wyskiel

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