How to Set Up a Freshwater Aquarium: Step-by-Step for Beginners

October 30, 2025 By Timmy Hyslop

Setting up your first aquarium is exciting and easier than you might think once you know the basics. Whether you dream of colourful tropical fish or a peaceful underwater scene, this guide will show you exactly how to set up a freshwater aquarium in Ireland.

At Timmy’s Pet Shop, we help beginner fish keepers create thriving tanks with the right setup, water care, and fish selection. Follow these simple steps to get started and enjoy a healthy, happy aquarium at home.

Why Choose a Freshwater Aquarium?

Freshwater aquariums are perfect for beginners. They’re affordable, easier to maintain than saltwater tanks, and offer plenty of fish species to choose from. With the right aquarium setup in Ireland, you can create a stunning feature for your home that’s relaxing to watch and rewarding to care for.

Step 1: Choose the Right Fish Tank

Pick the Perfect Size

A tank between 20–60 litres is ideal for beginners small enough to manage, yet large enough to maintain stable water conditions. Smaller tanks (under 20 litres) can fluctuate too quickly, making them harder to keep balanced.

Timmy’s tip: Start with a 40-litre tank if you have the space. It gives your fish room to swim and makes it easier to maintain consistent water quality.

Before you buy: Research what fish you’d like to keep so you can make sure they’re all compatible before stocking your tank.

Find the Right Spot

Place your tank on a sturdy, level surface away from direct sunlight. Too much sun can cause algae growth and temperature swings. Make sure the stand or cabinet can safely support the full tank weight remember, water weighs roughly 1 kg per litre.

Explore our range of Fish Tanks & Aquarium Starter Kits at Timmy’s Pet Shop.

Step 2: Gather Essential Equipment

To create a healthy aquarium, you’ll need a few key pieces of equipment.

Filter

A good aquarium filter removes debris and toxins, keeping your water clean and your fish healthy.

Internal filters are the most common option in Europe and are perfect for beginner and medium-sized tanks. They’re easy to maintain and provide reliable filtration. Canister filters, on the other hand, are ideal for larger aquariums as they offer stronger flow and greater capacity for filter media.

Heater & Thermometer

Most tropical fish need temperatures between 24–28°C. Use a submersible heater with a thermostat and a reliable thermometer to keep the temperature consistent.

Lighting

LED aquarium lights are efficient and enhance the natural colours of your fish. Choose a light with a day/night setting to mimic a natural environment.

Air Pump & Decorations

An air pump helps circulate oxygen, while plants, rocks, and ornaments provide hiding spots and create a natural look.

Shop Aquarium Filters, Heaters & Lighting online or in-store at Timmy’s.

Step 3: Set Up the Tank

Clean the Tank

Before setting up, rinse the tank with warm water and a soft cloth no soap or chemicals.

Add Substrate

Rinse gravel or sand thoroughly before adding it to your tank. Spread it evenly, about 2–3 cm deep.

Pro tip: Create a slight slope from back to front for a natural look.

Install Equipment

Add your filter, heater, air pump, and decorations before filling with water. Make sure everything is stable and secure.

Step 4: Add Water and Treatments

Fill the Tank

Slowly pour in dechlorinated water, using a bowl or plate to prevent the substrate from shifting.

Use Water Conditioners

Tap water contains chlorine and heavy metals that harm fish. Use a water conditioner to neutralise them before adding fish.

Test the Water

Check your pH, ammonia, nitrite, and nitrate levels. Aim for:

pH:5–7.5
Ammonia/Nitrite: 0 ppm
Nitrate: below 20 ppm

Pick up your Water Conditioners & Test Kits at Timmy’s Pet Shop.

Step 5: Cycle the Aquarium

Before adding any fish, it’s important to understand the nitrogen cycle the natural process that keeps your aquarium water healthy and safe.

When fish produce waste or leftover food breaks down, ammonia is released into the water. Beneficial bacteria then convert this ammonia into nitrite, and finally into nitrate, which is far less harmful.

This cycle helps maintain safe water conditions for your fish by breaking down toxins naturally. New tanks need a few weeks to build up these good bacteria, so it’s best to stock fish gradually rather than all at once.

Timmy’s tip: Keep testing your water regularly during the first month to ensure ammonia and nitrite levels stay low. If levels rise, perform small water changes until they stabilise.

Step 6: Choose Your Fish

Best Fish for Beginners

When starting out, choose hardy species that can tolerate small changes in water quality while your tank settles.

If you’re setting up a tropical aquarium:

Tetras – peaceful schooling fish that do well in groups.
Rasboras – small, colourful, and very hardy.
Danios (e.g. Zebra Danios) – active swimmers that handle new tank conditions well.

If you’re setting up a cold-water aquarium:

Goldfish – classic beginner fish, but make sure your tank is large enough.
White Cloud Mountain Minnows – small, hardy, and ideal for unheated tanks.

Stocking Tips

Introduce fish gradually to avoid sudden spikes in water quality. Always research compatibility before mixing species.

Browse our Tropical Fish & Accessories to find your perfect starter fish.

Step 7: Feed Your Fish

Choose Quality Fish Food

Feed a mix of flakes, pellets, or frozen foods for balanced nutrition. Avoid overfeeding uneaten food can pollute the tank.

Timmy’s tip: Feed once or twice a day, only what your fish can eat in 30 seconds.

Shop Tropical Fish Food at Timmy’s Pet Shop.

Step 8: Maintain Your Aquarium

Consistency keeps your tank healthy.
Weekly: Change 10–20% of the water, test levels, and remove debris.
Monthly: Rinse filter media gently in tank water (never under the tap) and check your equipment.
Ongoing: Keep an eye on your fish look out for stress, dull colours, or unusual behaviour.

Common Issues

Cloudy water: This is common and perfectly normal in newly set-up tanks as beneficial bacteria establish. It usually clears on its own after a few days. If it persists, check your feeding amounts and water parameters.
Algae growth: Limit tank light to 8–10 hours a day under normal conditions. If algae becomes excessive, reduce lighting to 2–3 hours a day or turn it off completely for a couple of days. Also make sure the tank isn’t in direct sunlight.

Beginner Tips for Aquarium Success

Start small and expand as you gain confidence.
Research fish compatibility before adding new ones.
Keep a simple maintenance log to track changes.
Be patient good tanks take time to mature.

Conclusion

Setting up a freshwater aquarium in Ireland is a fun and achievable project with the right guidance and supplies. Follow these steps from choosing your tank to cycling, stocking, and maintaining it and you’ll have a thriving aquatic environment in no time.

At Timmy’s Pet Shop, we stock everything you need: tanks, filters, heaters, water conditioners, tropical fish food, and more. Visit us in Waterford or shop online to get started today.

Shop Aquarium Essentials
Water Treatments & Test Kits
Fish Food & Accessories