Pet Fish Care for Beginners: A Healthy Tank Starts Here

A peaceful aquarium starts with a little preparation: choose the fish, build the right home, and learn what is happening in the water.

Plan the aquarium around the fish you want to keep, including their adult size and need for shelter.¹²

1. Choose the Fish Before You Choose the Tank

A fish that fits in a shop tank today may need much more room as an adult. Larger aquariums also give you a more stable environment than tiny bowls, which can change temperature quickly and leave little space for filtration.¹

Before buying, make a short species checklist:

• Adult size: how much swimming space will this fish eventually need?
• Water requirements: what temperature and water chemistry suit it?
• Social needs: does it need companions of its own species, or a separate home?
• Compatibility: will the proposed tankmates share suitable conditions and behaviour?¹²³

Avoid choosing a community purely by colour. Ask an experienced aquarist to check your proposed fish list against the aquarium you can provide. Crowding creates competition for food as well as water-quality problems.²

For a tropical freshwater setup, plan for a suitable filter, a thermostatically controlled heater and a separate thermometer. Check the actual temperature daily; the heater dial is not a measurement.¹

2. Cycle the Aquarium Before Adding Fish

An aquarium filter does more than catch visible dirt. Beneficial bacteria convert ammonia into nitrite, then nitrate. Ammonia and nitrite are harmful; nitrate is less toxic but still needs managing.¹

Growing this bacterial community is called cycling. Prefer a fishless cycle, with a controlled ammonia source and regular testing, rather than exposing live fish to the startup process.³

A tank full of clean-looking water is not automatically a cycled tank. Readiness depends on the filter processing the ammonia source and ammonia and nitrite returning to zero. A tank that has never received an ammonia source can read zero without being ready.³

Allow weeks, rather than promising yourself a fixed shopping date. The Merck Veterinary Manual notes that establishing a tropical aquarium biofilter can take up to eight weeks.³

Ask for a fishless-cycling plan appropriate to your equipment. Add fish gradually after cycling and keep checking the water as the biological filter adapts.⁴

3. Test the Water and Keep Cleaning Gentle

Illustrative testing setup: interpret your own samples using the instructions and colour chart supplied with your kit.

For a freshwater aquarium, track ammonia, nitrite, nitrate, pH and temperature. Aim for 0 mg/L ammonia and 0 mg/L nitrite; use species-specific guidance for the other readings.¹⁵

RSPCA Australia recommends ammonia and nitrite checks every two to three days during startup, then every one to two weeks once the biological filter is established. Test sooner if fish behaviour changes.⁴⁶

For routine care of an established tank:

• Change part of the water regularly. RSPCA Australia's starting guidance is 10–25% weekly, with the plan adjusted to your aquarium and readings.⁴
• Treat replacement tap water with aquarium conditioner that handles chlorine and chloramine, following the label, and match its temperature to the tank.⁴¹
• Use a dedicated aquarium bucket and siphon; keep soap and detergents away.⁴
• Gently rinse clogged filter media in removed aquarium water, rather than washing it under the tap.⁴

Worked example: a 20% change in a tank containing 60 litres of water means replacing 12 litres. Use actual water volume, allowing for gravel and decorations.

If waste readings rise or fish become unwell, seek advice promptly; routine maintenance percentages are not an emergency treatment plan.⁶

4. Feed for the Species and Make Room for Shelter

Buy food suited to your fish, including its feeding position. A bottom-feeding species may need sinking food rather than flakes that other fish eat first.⁷

Offer a measured portion and watch each fish eat. Remove leftovers. Overfeeding adds waste to the aquarium, so a fish approaching the glass is not a reason to keep adding food.⁵⁷

Build the habitat around behaviour too. Suitable plants, driftwood and hides provide shelter; leave open swimming areas, and avoid decorations with sharp edges or holes a growing fish could become trapped in.²⁵

Give fish a regular day-and-night cycle rather than leaving the aquarium light on continuously. RSPCA Australia recommends no more than 10 hours of aquarium lighting daily and at least eight hours of darkness for tropical fish.⁵

Going away? Leave pre-measured food and clear instructions with someone who can check the fish and equipment each day. Automatic feeders still need checking.⁷

5. Know When to Call a Fish Vet

Get to know your fish's usual appetite, breathing and swimming. A change from that baseline is more useful than expecting every species to behave alike.⁶

What you notice	Next step
Persistent gasping, rapid breathing or several fish suddenly affected	Check water and equipment immediately; contact a fish vet urgently
New loss of balance, marked lethargy or appetite loss	Test the water and arrange prompt veterinary advice
White spots, sores, damaged fins, swollen body or protruding scales	Seek a diagnosis rather than choosing treatment from appearance alone

These signs can involve water conditions or disease. A fish vet may need both the animal's history and water-quality information.⁶³ Some species, including bettas, normally visit the surface to breathe; persistent distress or a new change is the concern.⁶

Do not choose medicines, salt or temperature changes from a photo alone. Treatment safety depends on the species, water chemistry and other aquarium inhabitants.³

AI complements veterinary care; it does not replace it. It cannot measure your water or examine a fish. Use a test kit and a fish vet when health is in question.

6. Make Fish Care a Small, Steady Routine

Keep a simple log with the fish species, actual water volume, test readings, temperature, feeding and maintenance dates. Before seeking help, add when the problem began and whether anything changed recently.

Your daily check can be brief: observe the fish, check the thermometer and filter flow, and look for leftover food. Set reminders for testing and partial water changes, and write down the results.⁴⁵⁶

The aim is to recognise what is normal for your own aquarium and spot changes early.

Want to organise your pet-care questions? Start with PetCare AI — keep your fish's care details and observations ready for a clearer conversation with a fish vet.

Sources

Footnotes

1. RSPCA. Choosing an aquarium for pet fish. Aquarium size, filtration, cycling, water testing and temperature. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

2. RSPCA. Understanding pet fish behaviour and needs. Shelter, substrate and overcrowding. ↩ ↩² ↩³ ↩⁴

3. Merck Veterinary Manual. Management of aquarium fish. Cycling, assessment and treatment considerations. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

4. RSPCA Australia, authored by Dr Rob Jones (The Aquarium Vet). Why is water quality important when setting up a fish aquarium?. Testing schedules, partial water changes and filter care. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

5. RSPCA Australia, authored by Dr Rob Jones (The Aquarium Vet). How should I care for my tropical fish?. Equipment, feeding, habitat and lighting. ↩ ↩² ↩³ ↩⁴ ↩⁵

6. RSPCA. Pet fish health. Healthy behaviour, warning signs and specialist veterinary care. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

7. RSPCA. What to feed your fish. Species-appropriate food and holiday care. ↩ ↩² ↩³