Aquarium size
Bigger is better when it comes to aquariums, so go for more space than the minimum required. Larger volumes have more stable temperatures and water conditions. Only get a tank larger than 45 x 30 x 30cm (about 40 litres).
Remember to think about how big your fish will grow. Some adult fish grow very large, making them unsuitable as pets – for example, some catfish varieties (the red tail, shovelnose, pangasius), giant gourami and pacu.
Bear in mind the tank capacity for the size of fish you want to keep. Too many fish in a tank will pollute the water, which can lead to disease and death. Also, good oxygen exchange is essential: with too many fish in the tank, there will not be enough oxygen.
There are guidelines for the volume of water to be allowed per length of fish. For example, for tropical fish:
- Allow 1.5–2 litres of water per 1cm of tropical fish length (excluding their tails)
- Goldfish require more space, so: Allow 2 litres of water per 0.5cm of goldfish length
However, these should only be used as guidelines because water quality is affected by many factors, including temperature, water source, filtration power, how well you tend to the tank and more.
Working out tank volume
In calculate the volume of a tank before buying it, you can use this simple technique:
- width (cm) x depth (cm) x height (cm) / 1000 (volume)
For example, a tank measuring 60cm wide by 30cm tall by 30cm deep has a volume of 54 litres.
Aquarium shape
The surface area of the tank is vital because this is where oxygen diffuses into the water: wide tanks are better than tall tanks as they have a larger surface area for the water volume. Also add aeration equipment such as an air bubble stone, which agitates the surface of the aquarium. This will increase the amount of oxygen in the water.
Position
Don't put your aquarium near heat sources like direct sunlight and radiators and make sure it is on a sturdy surface. When an aquarium of the size needed, they can become surprisingly heavy. Consider pollutants in the air – cigarette smoke or aerosol sprays can be toxic to fish so this might be a factor when deciding where to locate your tank. An aquarium with a lid can help in preventing some pollution.
Aquarium filters
Filters are vital for removing waste from the tank, keeping your tank clean. Fish pee and poo in their water, so build-up of toxins can happen very quickly. No fish should be kept in tanks without a well set up and maintained filter.
Mechanical filtration is where particles are trapped so they can be removed. Biological filtration is more complex. Fish release ammonia into the water, which is toxic and must be dealt with. A working biological filter allows beneficial bacteria to grow, which break down waste naturally. Ammonia is converted to nitrite, which is also toxic, and then eventually to nitrate, which is safer. However, in high levels, nitrate can also cause problems for fish. This is why you need to carry out weekly 30% water changes to dilute the waste products your biological filter cannot break down.
Water changes
Leaving the fish in the tank, remove ten percent of the water with a siphon. Make sure you swish the filter sponge/media in the aquarium water you have removed as this clears the sponge of solids, but never wash it under the tap as you’ll kill the beneficial bacteria.
You must also keep the filter parts clean so that the filter runs smoothly and efficiently. This includes removing and cleaning the impeller.
Chlorine present in tap water is dangerous to both fish and bacteria. As such, it’s vital to add a dechlorinating product to the new water or leave it standing for 24 hours for the chlorine to leave the water.
When refilling the tank, you don’t want the new water to be a different temperature to that in the tank as this will shock the fish. It is a good idea to get a separate fish tank heater to heat the water before you add it.
You can’t determine the quality of the water properly just by looking at it: clear water doesn’t always mean healthy water. Instead, buy testing kits and check the water quality once a fortnight. Kits for ammonia and nitrite are essential – not optional extras.
The safe levels of these are:
- 0mg/L of ammonia
- 0mg/L of nitrite
If your tests show that the waste levels are higher than this, you’ll need to change half of the water every day and keep testing until conditions improve. If the chemical waste levels don’t decrease over time, then you will need to make steps to improve the water quality. Ask your aquatics shop for help with this.
Cycling a new fish tank
Fish tanks take time to establish because you need bacterial colonies to grow in the filtration system. It’s therefore strongly advised that new owners use ‘fishless cycling’ when starting up an aquarium. This involves running the tank filter for some time before adding any fish.
At the beginning, you will need to ‘seed’ the tank with a product to kick-start the growth of bacteria that are essential for keeping your water clean and suitable for fish once they arrive. Alternatively, you can use some filter media from a mature tank (as long as it is disease free) and add that to your filter.
During cycling, you should test your water every other day. Only add fish when there has been a spike in the levels of ammonia and nitrite, followed by a return to zero. There is no exact rule for how long cycling will take but it will be at least two weeks. Reputable retailers will ask that you bring in a water sample so they can test it to see if the tank is ready to add fish.
Fishless cycling prevents fish coming to harm from the spike of ammonia or nitrite. It also takes time, which is great because it allows you to practise maintaining your tank without bothering any fish.
Temperature
Goldfish need to be kept within 10–21ºC, so a heater isn’t normally necessary. However, if you are concerned about temperature swings, you could include a heater, set at the lower limit of the range.
With tropical fish, you must include a tank heater and set it to the correct temperature for the species. For example, guppies can tolerate 22–28ºC, while loaches need to be kept at 18–26ºC. You must research the temperature requirements of the fish species you want to keep. Go to The Ornamental Aquatic Trade Association (OATA) for more information.
All heaters must be controlled by a thermostat. Fish tank heaters are available with built-in thermostats. Just as with any electrical equipment, thermostats and heaters can fail, so use a digital thermometer and check the temperature every day.
Lighting
We recommend using artificial lighting during the day so the fish have a steady light cycle, just as they would in the wild.
A light cycle of eight to 10 hours a day, switched off at night, is suitable for most species. Don’t place the tank by a window as this can raise the water temperature dangerously high.
Settling in your fish
When the fish are being prepared for transport, make sure there is more air in the bag than water and that the fish are not overcrowded. Ideally, you want 2/3 air and 1/3 water in the bag. If the weather is cold, don’t hesitate to ask the shop to wrap the bags in paper to help prevent sharp temperature drops. Take the fastest route home to minimise transport and packaged time.
When introducing the fish to your aquarium, turn off the lights and leave the bag in the water for half an hour to allow the water in the bag to come to temperature. Then use a net to transfer the new fish to your tank and throw away the water from the bag. Keep the tank lights off for the rest of the day so that the fish can rest and explore in their own time. The following morning, you can turn on the lights and check on your fish.
Unsuitable aquariums
Decorative or ‘fun’ tanks, like goldfish bowls, jars, or children's tanks, have not been designed with fish welfare in mind.
- their small size isn't big enough – for example, goldfish require at least 60 litres of water each. Small volumes don't provide a stable environment for the fish to live in
- there isn't enough space for an efficient filter, so waste products can't be removed
- the low surface area means that not enough oxygen will be absorbed into the water
temperature levels can alter rapidly, which can cause stress and even death
Ponds
We don't recommend releasing fish into outdoor ponds as they can cause damage to wildlife through hunting and could easily spread disease.
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