Plan a healthy fish tank before you buy a single fish.

Stocking calculator

How many fish fit, and can they live together? Bioload, water, groups and compatibility in one check.

Compatibility checker

Compare two or more species and see exactly why they work or clash.

Tank mates finder

Good, risky and bad tank mates for every species, with a reason for each.

My tanks

Save your tanks, log water tests and get water change reminders. Stays in your browser.

Aquarium calculators

Volume, gravel, heater size, filter flow, water changes and unit conversions.

Equipment checklist

Everything a new tank needs, with heater, filter and gravel sizes for every common tank.

Compatibility chart

The 30 most popular fish on one printable chart.

Angelfish

15 cm (5.9 in) · 29+ gallons

The angelfish is a tall, graceful South American cichlid that grows about 15 cm (6 in) long and even taller with its fins. It makes a classic community centerpiece, but it needs a tall tank and will eat small fish such as neon tetras.

Betta fish

6.5 cm (2.6 in) · 5+ gallons

The betta is a colorful, long-finned labyrinth fish that breathes air at the surface and is usually kept alone. Give it a heated, filtered tank of at least 5 gallons (19 L), ideally 10 (38 L), with gentle flow and never another male betta.

Bristlenose pleco

12 cm (4.7 in) · 20+ gallons

The bristlenose pleco is a small, hardy catfish that stays around 4–5 inches (12 cm) and grazes algae day and night. It's one of the best algae eaters for tanks of 20 gallons (76 L) or more, but it needs driftwood, a cave and vegetables, not just leftover algae.

Bronze corydoras

7 cm (2.8 in) · 20+ gallons

The bronze corydoras is a hardy, peaceful South American catfish that spends its day sifting the bottom for food. It is one of the easiest corys for beginners, but it needs a group of 6 or more, soft sand and its own sinking food.

Cherry shrimp

3 cm (1.2 in) · 5+ gallons

Cherry shrimp are small, hardy freshwater shrimp bred in red, blue, yellow, orange, green and black. They graze algae and leftovers and breed readily in a planted tank, but they need stable water, no copper and no fish big enough to eat them.

Common goldfish

30 cm (11.8 in) · 75+ gallons

The common goldfish, including the comet and shubunkin, is a hardy, fast cool-water fish that often reaches 12 in (30 cm) or more. It needs a very large tank, at least 75 gallons (284 L) for one, or a pond, plus strong filtration and no tropical tankmates.

Common pleco

40 cm (15.7 in) · 150+ gallons

The common pleco is the armored sucker catfish sold as a small algae eater, but it grows to 12–18 inches (30–45 cm) or more. An adult needs a tank of at least 150 gallons (570 L) and 6 ft (180 cm) long, so it suits very few home aquariums.

Dwarf gourami

7.5 cm (3 in) · 15+ gallons

The dwarf gourami is a 3 in (7.5 cm) labyrinth fish whose males shine electric blue and red. It suits a calm, planted community tank of 15 gallons (57 L) or more. Keep only one male, and buy with care: many farmed fish carry disease.

Fancy goldfish

15 cm (5.9 in) · 20+ gallons

Fancy goldfish are slow, round-bodied goldfish such as orandas, ryukins and black moors. They are messy cool-water fish that need about 20 gallons (76 L) for the first fish plus 10 gallons (38 L) for each extra, strong filtration and no tropical tankmates.

Guppy

5 cm (2 in) · 10+ gallons

The guppy is a small, colorful livebearer and one of the easiest fish to start with. Males have big flowing tails, while females are larger and plainer. Keep guppies in hard, alkaline water and plan for babies, because they breed nonstop.

Neon tetra

3.5 cm (1.4 in) · 15+ gallons

The neon tetra is a tiny, peaceful schooling fish with a glowing blue stripe and a red rear half. It is one of the easiest and most popular community fish, but it needs a group of 8 or more and a mature, stable tank.

Nerite snail

2.5 cm (1 in) · 5+ gallons

Nerite snails are small, patterned snails that scrape algae off glass, rocks and leaves without harming plants. Their eggs can't hatch in fresh water, so they never overrun a tank, but they need hard water, enough algae to eat and a tight lid.

Ammonia in a fish tank: causes, symptoms and how to fix it

High ammonia in a fish tank? Do these emergency steps first, then find the cause. Safe levels, a pH and temperature toxicity table, symptoms and prevention.

Aquarium nitrogen cycle explained, with week-by-week readings

How the aquarium nitrogen cycle turns fish waste into ammonia, then nitrite and nitrate, which microbes do the work, week-by-week readings and when it is done.

Aquarium water parameters chart: safe ranges for freshwater

Safe ammonia, nitrite, nitrate, pH, GH, KH and temperature levels for freshwater tanks, how to test them, and how to fix each one without shocking your fish.

Best algae eaters by tank size, including betta tanks

The best algae eaters for 5 to 55+ gallon tanks, which algae each one actually eats, safe picks for betta tanks, and the ones that outgrow most aquariums.

Best fish for beginners: hardy picks by tank size

The best fish for beginners, sorted by tank size, with the minimum tank, group size and temperature for each, plus popular fish new keepers should avoid.

Easy aquarium plants for beginners: 8 that grow without CO2

Eight easy aquarium plants that grow without CO2: light needs, how to attach or plant each one, when to use root tabs, and which fish eat plants.