Coldwater Aquarium Setup Guide

Learn how to set up a perfect coldwater aquarium for goldfish and other hardy species.

Coldwater aquariums are a great way to enjoy keeping fish without the need for a heater. They’re ideal for beginners, families, or anyone who wants a low-maintenance, beautiful aquarium at home. Whether you’re starting with a small tank or a larger aquarium, the right setup makes all the difference to your fish’s health and happiness. At Birchwood Aquatic Centre, we stock everything you need — tanks, filters, water treatments, décor, and, of course, healthy hand-selected coldwater fish.

Step-by-Step Coldwater Aquarium Setup

1. Choose the Right Aquarium Size

While small tanks may seem easier, larger tanks are actually more stable and forgiving for beginners.

  • For a single fancy goldfish, we recommend at least 120 litres just remember this will need upgrading as your fish grow (goldfish grow larger than most people assume).
  • For common or comet goldfish, 200+ litres is ideal as they grow quickly.
  • Always allow plenty of swimming space and surface area for oxygen exchange.


2. Pick Suitable Equipment

Coldwater fish still need filtration and good water movement.

  • Filter: Use an internal or external filter sized for your tank volume.
  • Lighting: A low-heat LED light helps plants thrive and enhances viewing.
  • Air pump: Increases oxygen and prevents stagnant water.
  • Gravel or substrate: Rinse before use to keep the water clear.


3. Add Décor and Plants

Choose smooth ornaments and silk or live plants to create hiding spots and enrichment. Avoid sharp edges that could damage fins. Hardy live plants like Anubias, Elodea, and Java Fern can thrive in cooler water.


4. Fill and Treat the Water

Always use dechlorinator before adding water to the tank. Chlorine and chloramine in tap water can harm fish and beneficial bacteria.


5. Cycle the Aquarium

Before adding fish, your aquarium must go through the nitrogen cycle. This process builds up beneficial bacteria that break down fish waste (ammonia and nitrite) into safer nitrate.
 Learn more in our How to Cycle Your Aquarium guide


6. Introduce Fish Slowly

Once your water tests show 0 ammonia and 0 nitrite, you can begin adding fish. Start with just a few and increase numbers gradually to avoid stressing the biological filter.


7. Regular Maintenance

Perform weekly partial water changes (25–30%) and clean filter sponges in old tank water (never tap water).

Best Coldwater Fish for Beginners

  • Fancy Goldfish (Oranda, Ryukin, Fantail)
  • White Cloud Mountain Minnows
  • Weather Loaches (Dojo Loach)
  • Zebra Danios (can live unheated in mild homes)

Visit our Best Coldwater & Goldfish Species Guide to discover more options.

Quick Setup Checklist

  • Tank (minimum 120L for goldfish)
  • Filter & air pump
  • Water conditioner
  • Gravel & decorations
  • Test kit (ammonia, nitrite, nitrate, pH)
  • Fish food & net
  • Weekly water change schedule

Frequently Asked Questions


No — coldwater fish like goldfish and minnows prefer unheated tanks. However, keep your aquarium away from radiators and direct sunlight to avoid temperature swings.


Ideally, wait 2–4 weeks to complete the cycling process. You can speed this up by using bottled bacterial starter or by adding mature filter media.


We don’t recommend it. Bowls are too small, lack filtration, and quickly accumulate waste. A proper filtered aquarium ensures clean, oxygen-rich water.


Do a 25–30% water change once a week and vacuum the gravel to remove uneaten food. Clean filters in tank water every 2–3 weeks.


Most thrive between 16°C and 22°C. Avoid sudden temperature changes — stability is key.


No — tropical species need consistent warm temperatures around 24–28°C, which would stress coldwater fish.


This is common during the cycling period and usually clears as bacteria establish. Regular partial water changes help.

Visit Birchwood Aquatic Centre

Pop into our Swanley store to browse aquariums, filters, live plants, and our beautiful selection of coldwater fish. Our expert team can help you design the perfect setup for your home.

 Birchwood Aquatic Centre, London Road, Swanley, Kent, BR8 7QD
 01322 664397

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