Aquarium Fish for Beginners: Setup and Care

Quick answer

Keeping fish healthy mostly comes down to keeping the water healthy. Start with a tank of at least 60–100 litres (about 16–26 US gallons) and a filter and heater sized for it. Then cycle the tank before any fish go in, so beneficial bacteria are in place to break down waste. After that: pick hardy, peaceful species, add them slowly, feed lightly and change some of the water every week.

What you need

Stand the tank on something sturdy and level that can take its full weight. Water weighs about 1 kg per litre (8.3 lb per US gallon), so even a medium tank is very heavy. Keep it out of direct sunlight, which brings on algae and temperature swings.

Cycling: the step beginners skip

Fish waste and leftover food give off ammonia, which is toxic. Beneficial bacteria convert ammonia into nitrite (also toxic) and then into nitrate. Nitrate is much less harmful and gets removed with water changes. That chain is the nitrogen cycle.

A new tank has none of these bacteria yet. Put a full load of fish in straight away and ammonia builds up until fish sicken or die. Fishkeepers call this "new tank syndrome".

To cycle a tank:

1. Set up the tank, filter and heater, and fill with dechlorinated water.
2. Add an ammonia source: a small pinch of fish food every day, or pure ammonia sold for fishless cycling.
3. Test every few days. Ammonia rises first, then nitrite, then both drop to zero as nitrate appears.
4. Once ammonia and nitrite have read zero for several days, the tank is ready.

Expect this to take 4–8 weeks. Bottled bacteria can speed it up. For a step-by-step version, read the aquarium nitrogen cycle, explained simply.

Hardy beginner fish

Go for peaceful species that forgive small mistakes. Look up adult size before you buy, because many fish in shops are juveniles.

Tropical (heated tank):

• Platies and mollies: colourful and hardy, and they breed readily.
• Zebra danios: active and tough. Keep six or more together.
• Neon or cardinal tetras: best added once the tank has matured. Keep in groups.
• Corydoras catfish: peaceful bottom dwellers that need a group and soft sand or smooth gravel.
• Bristlenose pleco: a small algae-eater, unlike common plecos, which grow very large.
• Betta: one male per tank, in at least 19 litres (5 US gallons) with gentle flow and a heater.

Coldwater (unheated):

• Goldfish: need far more space than people expect, produce a lot of waste, and do best with other goldfish rather than tropical species.
• White cloud mountain minnows: small and peaceful, and happy at cooler room temperatures.

Avoid as a beginner: common plecos, oscars and other large cichlids, red-tailed sharks in small tanks, and fin-nippers (such as tiger barbs) kept with long-finned fish.

Stocking slowly

Add a few fish at a time and wait a week or two between batches, so the bacteria can keep up with the extra waste. No single "inch per gallon" rule really works, since body size, activity and waste output all count. If in doubt, stock lightly.

Acclimatising new fish: float the bag for about 15 minutes to even out the temperature. Then add small amounts of tank water over another 15–20 minutes before netting the fish into the tank. Try not to pour shop water into your aquarium.

The best protection against bringing disease into your main tank is a separate quarantine tank for new arrivals.

Feeding

• Feed a good flake or pellet suited to the species, once or twice a day.
• Give only what gets eaten in about two minutes.
• A few times a week, mix it up with frozen foods such as bloodworm or brine shrimp, or blanched vegetables for plant-eaters.
• Healthy adult fish cope fine with a few days without food. Skipping a day is safer than overfeeding.

Weekly maintenance routine

1. Test ammonia, nitrite and nitrate (weekly at first, less often once things are stable).
2. Change about 20–25% of the water, using a siphon to clean the gravel as you go.
3. Treat the new water with conditioner and match its temperature.
4. Rinse filter media gently in old tank water, never under the tap, which kills the bacteria. Do not replace all the media at once.
5. Wipe algae off the glass and trim plants.
6. Check the heater and filter are working.

Spotting sick fish

Feeding time is a good moment to look your fish over every day. Warning signs include:

• Gasping at the surface or hanging near the filter outflow (often poor water or low oxygen)
• Clamped fins, hiding or loss of appetite
• White spots like grains of salt, a sign of ich; see ich (white spot) treatment
• Frayed or rotting fins, cotton-like growths, red streaks or ulcers
• Swollen body or raised scales
• Rubbing against objects

Whenever fish look unwell, test the water first. A lot of problems trace back to ammonia, nitrite or temperature, and a partial water change helps if the readings are off. For treatment, ask an experienced aquarium shop or a vet who knows fish, and follow the medicine's instructions carefully. Some treatments harm shrimp, snails or plants.

Ready to choose your first fish? You can browse fish and aquarium listings on Paalo.