Fish tank buying guide

You can't just wing it when it comes to picking an aquarium. It's important to take several factors into consideration before settling on a particular type of fish tank. Start by asking yourself a few questions to identify your needs:

• What type of aquarium do I want – freshwater or saltwater?

• What is my total budget?

• How many fish do I want and how big does the tank need to be?

• What kind of equipment do I need to take care of my fish?

The answers to these questions should help guide you towards the best model for your needs. So, let's take a closer look at these criteria.

There are two basic types of aquariums: saltwater tanks and freshwater tanks. The vast majority of fish owners have freshwater tanks which are much easier to keep than saltwater tanks. Beginners are recommended to keep individual aquariums designed to accommodate just one species of fish.

Fishkeeping can be an expensive hobby so it's important to decide how much money you're willing to spend. Budget is one of the most important factors when it comes to choosing a fish tank. The price of a fish tank all depends on its size, your choice of equipment and the type of fish you want to keep.

A fully equipped 120-litre fish tank plus fish will cost you several hundred pounds. While freshwater tanks are the least costly to purchase, reef tanks are by far the most expensive. 

If you're just getting started, it's best to go for a fish tank with a capacity of at least 120 litres, which is already a good-sized aquarium. If you want a saltwater fish tank, you will need a minimum volume of 300 litres. This is because the physio-chemical parameters of a fish tank are stabler and slower to change when you have a larger volume of water. This gives you a certain amount of leeway for minor mistakes. On the other hand, fish have a harder time settling into smaller tanks. 

The size of the fish tank will also depend on where you plan to put it and the space you have available. 

Freshwater aquariums

Freshwater fish are much easier for beginners as there are fewer parameters to monitor and the fish are less sensitive. There is another sub-category within freshwater aquariums:

• cold water aquariums are kept at temperatures of 18 to 20 °C. Many different varieties of goldfish will live happily in this type of fish tank. These fish are hardy and easy to keep;

• tropical aquariums are kept at temperatures of 24 to 30 °C. This type of fish tank is designed to recreate a specific environment (such as a river or lake) using plants and minerals.

Saltwater fish tanks

There are also two sub-categories of saltwater fish tanks: 

• marine fish tanks;

• reef fish tanks which mainly contain coral with a few fish.

Once again, there are a few factors to bear in mind. Start by working out a suitable budget bearing in mind that the larger the fish tank, the more expensive it will be to purchase and maintain. Remember – a fish tank isn't an ornament and can't be moved around. As such, you need to think carefully about: 

• the location of power sockets; 

• leaving enough space around the tank for cleaning; 

• picking a spot with no sun exposure;

• ensuring the floor can support the weight of the aquarium if you go for a large tank.

The final point is very important. Make sure to check that the floor of your building can withstand the weight of the tank before purchase. To estimate the weight of a fully equipped fish tank it is a good idea to multiply the weight of the water it is designed to contain (1 kg per litre) by 1.5.

How to size a fish tank

Rectangular, cylinder, flat-back hex... when it comes to design, the choice is entirely yours! However, the size of your tank depends on the number of fish you want to keep. It should be noted that in the world of fishkeeping, fish aren't measured in quantity or weight, but rather in centimetres. The golden rule is to allow for 1 cm of adult-sized fish per litre of water.

For example, a 120-litre aquarium containing about 100 actual litres of water can hold 100 cm of fish. If an individual fish is expected to reach 5 cm come adulthood, you can only fit 20 in your fish tank.

This rule applies to small fish measuring up to 5 cm. For any adult-size fish larger than 5 cm, it is recommended to allow 1 cm of fish per two litres of water. However, it's important to consider the variety of fish as some types require more space than others. 

Water volume isn't the only criterion to consider when it comes to fish tank size – some specialists recommend a length of at least 80 cm, even for small fish.

These days, most fish tanks come fully equipped but the quality of the accessories can vary. It's also possible to buy a bare fish tank and add your own equipment; for example, filters, pumps, lighting and heating systems.

If you buy an unequipped fish tank, check that it is a standard size that will allow you to fit a standard lighting system.

Standard fish tank characteristics

You will probably have realised by now that there are four essential pieces of equipment in a fish tank: a lighting system, filters, air pumps and a heating system.

Aquarium lighting is designed to provide enough light to aquatic plants and to allow us to enjoy the fish tank décor. It won't usually be possible to add additional tube lights to an aquarium. The aquarium lighting system therefore needs to be suited to your needs from purchase. This means the number and power of your LED lights or tube lights should be matched to the size of the tank. For example, a 120-litre fish tank will need about 50 W.

Tube lights and LED lights are kept in a special housing. This should be easy to access for cleaning and maintenance, and also provide the correct amount of light. It's also important to be able to pivot or remove the lighting system for cleaning. Tube lights, in particular, mustn't block access to the interior of the fish tank. 

The lighting system will play a big part in the price of an aquarium. It is important to go for a high-quality system.

Filtration is another important aspect of fishkeeping. Filters help to eliminate organic waste which can pollute water. Without a filter, you'll need to change your fish tank water daily. You can choose between a few different types of fish tank filter. 

The flow rate must be chosen according to the size of the fish tank. For a 120-litre tank, you'll need a pump able to process 250 to 300 litres of water per hour.

Air pumps and bubblers aren't really essential items in most cases. These pumps are designed to create bubbles to increase the amount of oxygen in the water. The bubbles themselves don't provide oxygen but rather create movement at the surface of the water to increase oxygen levels.  

For a 120-litre tank, go for a pump with a minimum flow rate of 160 litres per hour.

You only really need heating if you want to keep tropical fish. The power of the system needs to be weighed up against the external temperature of the tank and the desired water temperature, which usually sits around 25°C.

Around 100 to 150 W should suffice. For a room kept at 19°C, account for about 1 W per litre of water.