How to set up a marine aquarium

With the right planning and enough research, setting up your marine fish tank doesn't have to be challenging. In this section, we'll walk you through the process, from choosing a tank to stocking your fish, step-by-step.

1: Choosing your marine aquarium

It's a common misconception that beginner aquarists should start with a small tank. Saltwater aquariums are more stable when larger, as changes in the water quality are slowed. A tank of around 200-300L is a great starting point. However, a small nano reef can work with careful planning.

Rectangular aquariums are the most practical choice, thanks to the large amount of swimming space, and the additional surface area for gas exchange. Some unusual shaped tanks can be suitable, although it's important to bear in mind that aquascaping and lighting may be complicated.

Tip: For active swimming species, such as tangs, a space of at least 120cm is best.

Explore our range of marine aquariums to find the perfect system for your living space.

Marine aquarium with marine fish, corals, and rockwork.
Larger tanks allow for more stable water parameters and easier maintenance

2: Planning the location

Saltwater tanks are extremely heavy once filled, so it's essential to situate them on a purpose-built cabinet. These cabinets don't just support the weight safely, but also provide hidden storage for equipment.

Avoid positioning your aquarium in direct sunlight, to prevent the growth of algae, and keep away from radiators and draughty areas. An accessible spot in your living room or office is ideal, or anywhere you can enjoy the view whilst allowing easy access for maintenance.

Tip: Make sure that the floor is level and strong enough to handle the weight before filling the tank.

3: Filters and protein skimmers

Success with a marine system relies on three cores of filtration working simultaneously. The first is a protein skimmer, which removes dissolved waste before it has a chance to break down, keeping the water clear. As well as this, biological media such as live rock or ceramic blocks provide a home for beneficial bacteria that converts toxic ammonia into safer compounds. Chemical filtration, usually activated carbon or phosphate remover, helps to polish the water and prevents algae. 

Tip: Select a skimmer that is suitable for at least double your tank's capacity for the best results.

Browse our selection of skimmers and filter media to create a healthy ecosystem.

Swell Reef Edge Protein Skimmer
Protein skimmers efficiently remove waste to keep your water clear

4: Water movement

In the natural ocean, water is constantly moving, providing oxygen and pushing waste away. Corals also rely on currents and turbulence to survive. You'll need at least one wavemaker to recreate this, possibly more depending on the size of the tank. 

Fish only tanks require gentle circulation, but reef tanks thrive with strong and varied flow. Some wavemakers allow you to control wave patterns and intensity, making them ideal for these aquariums.

Tip: Position wavemakers so the water flows around rather than directly at corals to prevent dead spots.

5: Heating and temperature requirements

Saltwater fish require stable temperatures, typically between 24-26°C. A heater paired with a thermometer is an essential. A popular choice is a titanium heater pared with an external controller, thanks to its precision and durability.

Tip: Don't rely on a heater alone, always double check with a thermometer to avoid dangerous fluctuations.

6: Lighting a marine tank

Marine lighting isn't just for viewing, it's life support for corals, clams, and anemones. Fish only tanks only need standard LEDs for viewing, but lighting is optional. However, if you have a reefscape, you'll need high powered controllable LEDs that mimic natural sunlight, and will bring out colouration.

Some high-end reef lights even allow you to set sunrise and sunset cycles, creating a natural and automated rhythm for your tank.

Tip: Limit lighting to 8-10 hours per day to reduce excessive algae growth.

Shop our range of marine lighting to find the best LEDs for your tank.

Marine aquarium and marine-spec LED lighting with mounting set, as well as rockwork, fish, shrimp, and corals.
Reef-spec LED lighting is essential for supporting coral growth

7: Substrate and decorating

Substrate is the foundation of your aquascape. Aragonite sand or crushed coral are an excellent choice as they help to stabilise pH while keeping a natural aesthetic. Keep your substrate layer shallow, ideally around 2-3cm to avoid a build up of nutrients.

Rockwork provides biological filtration as well as adding a natural and decorative feature. Dry or live rock can be stacked and shaped to form caves, arches, and ledges. This gives fish enough space to hide, alleviating stress, and gives coral space to grow.

Tip: Build a structure that allows water to freely circulate, rather than constructing solid rock walls.

Large marine aquarium with fish, rockwork, corals and starfish.
Marine decorations are usually kept as simple rockwork to showcase corals

8: Preparing the saltwater

Saltwater aquariums require carefully mixed saltwater. Starting with reverse osmosis (RO) water, which is free from impurities, add a high-quality marine salt mix, stirring until dissolved. Measure the salinity of the water using a refractometer. The ideal reading should be between 1.023 and 1.026 specific gravity.

Tip: Always mix salt into water, never water into salt, and allow 24 hours of circulation before use.

Stock up on marine salts to prepare your water correctly.

9: Stocking your marine tank

It's important to be patient when adding livestock to your new aquarium. Allow your tank to fully cycle before introducing any fish or coral.

Beginner friendly fish include:

  • Clownfish - hardy, colourful, and full of personality, perfect for first-time marine fishkeepers.
  • Cardinals - peaceful shoaling fish that add movement to your tank.
  • Gobies - small bottom dwelling fish that sift sand and keep your substrate clean.
  • Chromis - active schooling fish that bring plenty of movement and energy.

Once your tank has matured you may consider adding more advanced species such as tangs, which need active and dwarf angelfish.

Invertebrates are excellent for algae control, including:

  • Hermit crabs - fascinating crabs that eat leftover food and detritus.
  • Cleaner shrimp - helpful for picking parasites from fish.
  • Turbo snails - natural algae grazers that keep rockwork and glass clean.

For corals, it's recommended to start with hardy soft corals like mushrooms and zoanthids before progressing to large-polyp stony (LPS) corals.

Tip: Introduce livestock gradually, adding only a few creatures at a time to avoid sudden water quality issues.

Browse our selection of marine livestock today to get started on planning your reef.

Blue and yellow striped marine fish in an aquarium with corals
Stock your aquarium slowly and carefully to avoid harmful fluctuations in water quality

10: Maintenance routine

Maintaining a saltwater tank is an essential for it to flourish. A good cleaning schedule includes:

  • Weekly water testing: testing for ammonia, nitrite, nitrate, pH, and salinity
  • Partial water changes of 10-20% every week or two using pre-mixed saltwater
  • Clean the skimmer and replace filter media as needed
  • Wipe the glass with a scraper or magnet as required
  • Vaccum detritus from the sand

Tip: an auto top-up system automatically replaces evaporated water, keeping salinity levels stable.

Try our maintenance tools to keep your tank in the best condition.

What do I need to set up a marine fish tank?

To get set up, you'll need:

  • Marine tank and cabinet
  • Lighting (reef specific for keeping corals)
  • Heater and thermometer
  • Protein skimmer
  • Filter
  • Wave maker
  • Substrate
  • Live rock
  • Marine salt
  • Hydrometer/refractometer
  • RO water
  • Fish food
  • Net and cleaning tools

Frequently asked questions

How long should I wait before adding fish?

Ideally, it's recommended to wait at least 4-6 weeks before adding livestock, or until the ammonia and nitrite levels consistently read zero when testing. Bottled bacteria and live rock may help to speed up this process.

Do I need a sump?

Sumps are not essential, but are highly recommended for tanks over 200L. A sump adds extra water volume, hides equipment, and makes your system more stable.

Why can't I use tap water?

Tap water contains chlorine, phosphates, and heavy metals that are harmful to corals and fish. RO water is the only safe option.

How do I maintain a marine system long term?

Consistency in maintenance is key. Stick to a routine that fits your schedule of testing, water changes, and equipment checks, and always add new livestock slowly and with caution.

Clownfish in a marine aquarium with anemone.
With the right planning and care, you can easily create a thriving marine system

Ready to set up your marine tank?

A well-maintained saltwater system brings the beauty of the ocean right into your home. With the right planning, equipment, and maintenance, you can easily build a reefscape full of thriving aquatic life.

Explore our full range of marine products today, from aquariums to equipment, salt and even marine fish.