Freshwater · Beginner
Betta
Betta splendens
Bettas are labyrinth fish that breathe from the surface, but they still need a heated, filtered aquarium, not a vase. A 5-gallon tank is a minimum for a single male.
Min. tank: 5 gal
Care notes →Freshwater aquariums
Most first tanks are freshwater: heated tropical communities or, less often, coldwater goldfish. The pattern is the same. Cycle the filter, match adult size, and ignore bowls. Here are the freshwater species we cover, plus the setup guides that go with them.
New to the hobby? Read beginner freshwater aquarium setup and how to cycle a fish tank. Looking at a 20-gallon kit? See stocking a 20-gallon tank or try the stocking calculator.
Freshwater species
Freshwater · Beginner
Neon tetra
Paracheirodon innesi
Keep neon tetras in a school of at least 6, and plan on 8 to 12 in a 20-gallon tank. Adults stay under 1.5 inches. A 10-gallon is the minimum for a small school. Hold the water at 72 to 78°F, soft and slightly acidic (pH 5.5 to 7.0), with plants and dim light.
Min. tank: 10 gal
Care notes →
Freshwater · Intermediate
Cardinal tetra
Paracheirodon axelrodi
Cardinal tetras (Paracheirodon axelrodi) are Amazon schoolers with a full red stripe from snout to tail. Plan a school of eight to ten in a planted 20-gallon with soft, clean water, not a neon-sized squeeze in a 10.
Min. tank: 20 gal
Care notes →
Freshwater · Beginner
Black neon tetra
Hyphessobrycon herbertaxelrodi
Black neon tetras (Hyphessobrycon herbertaxelrodi) stay about 1.5 inches. Keep at least six in a cycled 15-gallon, or eight to ten in a 20, with plants, moderate flow, and water at 72 to 80°F. They handle ordinary tap water better than neons or cardinals do.
Min. tank: 15 gal
Care notes →
Freshwater · Beginner
Glowlight tetra
Hemigrammus erythrozonus
Glowlight tetras (Hemigrammus erythrozonus) grow to about 1.5 inches and carry a thin orange-red line from nose to tail. Keep six or more in a cycled 15-gallon, or eight to ten in a 20, at 74 to 82°F. Dark substrate, floating plants, and dim light make the line show.
Min. tank: 15 gal
Care notes →
Freshwater · Intermediate
Rummy-nose tetra
Hemigrammus bleheri / H. rhodostomus / Petitella (trade mix)
Rummy-nose tetras sold in shops are a trade mix of Hemigrammus bleheri, H. rhodostomus, and Petitella names. Care is the same lane. Adults reach about 2 inches. How many fit in a 20-gallon? Eight to ten in a 20-gallon long, and ten still leaves room for six peppered cories on the bottom. Plant it well and keep the water soft to moderate and clean. A bright red nose and black-and-white striped tail are the ID. A pale nose often means stress, a new tank, or dirty water.
Min. tank: 20 gal
Care notes →
Freshwater · Beginner
Harlequin rasbora
Trigonostigma heteromorpha
Harlequin rasboras (Trigonostigma heteromorpha) are peaceful midwater schoolers with a black triangle on the rear body. Plan six to ten in a planted 20-gallon; a 10 is a tight floor for six, not a comfortable home.
Min. tank: 20 gal
Care notes →
Freshwater · Beginner
Celestial pearl danio
Danio margaritatus
Celestial pearl danios (Danio margaritatus), also sold as galaxy rasboras, are ~1-inch nano schoolers for a planted 20-gallon. Keep 10-15 with gentle flow, dense plants, and dark substrate. A 10-12 gallon long is a tight species-only floor, not a comfortable community home.
Min. tank: 20 gal
Care notes →
Freshwater · Beginner
Ember tetra
Hyphessobrycon amandae
Ember tetras (Hyphessobrycon amandae) are ~0.7-1 inch orange nano schoolers for a planted 10-20 gallon. Keep 10 or more with gentle flow, plants, and micro foods. A 10-gallon works for a species school; use 20 gallons if you mix in other fish.
Min. tank: 10 gal
Care notes →
Freshwater · Beginner
Chili rasbora
Boraras brigittae
Chili rasboras (Boraras brigittae) are ~0.6-0.8 inch red nano schoolers for a densely planted 10-20 gallon. Keep 10-12 or more with soft acidic water, gentle flow, dark substrate, and micro foods. A 10-gallon is a species-only floor; use 20 gallons if you mix in other fish.
Min. tank: 10 gal
Care notes →
Freshwater · Beginner
Honey gourami
Trichogaster chuna
Honey gouramis (Trichogaster chuna) are small, peaceful labyrinth fish for a planted 10-gallon solo or a 20-gallon pair or community. They are not dwarf gouramis. Shops often mislabel orange dwarfs as honey.
Min. tank: 10 gal
Care notes →
Freshwater · Beginner
Pearl gourami
Trichopodus leerii
Pearl gouramis (Trichopodus leerii) grow to about 4 to 5 inches and are calm enough to be the centerpiece of a community tank. Keep one in a cycled 20-gallon long, or a pair or one gourami plus a school in a 29. They want warm water at 77 to 82°F, floating plants, gentle flow, and a lid that keeps the air above the water warm.
Min. tank: 20 gal
Care notes →
Freshwater · Beginner
Dwarf gourami
Trichogaster lalius
Dwarf gouramis (Trichogaster lalius) grow to about 3 to 3.5 inches and are the most common gourami in shops. One male fits a cycled 10-gallon, and a 20 gives him room for a school or two females. Keep them at 75 to 80°F with floating plants and gentle flow. Farmed fish often carry dwarf gourami iridovirus, so buy carefully and quarantine.
Min. tank: 10 gal
Care notes →
Freshwater · Beginner
Cherry barb
Rohanella titteya
Cherry barbs (Rohanella titteya, still sold as Puntius titteya) are the peaceful Sri Lankan barb for a planted 20. Keep six or more so males color up deep red and any nipping stays in-group.
Min. tank: 20 gal
Care notes →
Freshwater · Beginner
Cherry shrimp
Neocaridina davidi
Cherry shrimp (Neocaridina davidi) are beginner invertebrates if the tank is cycled and copper-free. A starter colony of 10+ needs about 5 gallons; 10 gallons is easier. They need minerals for molting, not a second fish-page clone.
Min. tank: 5 gal
Care notes →
Freshwater · Beginner
Amano shrimp
Caridina multidentata
Amano shrimp (Caridina multidentata) are beginner invertebrates in a cycled, copper-free tank. Plan a crew of 3–6 in a 20-gallon planted setup. Adults reach about 1.5–2 inches. Feed biofilm plus wafers. Do not expect a freshwater breeding colony.
Min. tank: 20 gal
Care notes →
Freshwater · Beginner
Nerite snail
Neritina / Clithon / Vittina (trade mix)
Nerite snails sold in shops are a trade mix of Neritina, Clithon, and Vittina. Zebra, olive, horn, and tiger are shell patterns with the same care. Beginner livestock if the water is hard enough. Adults reach about 0.75–1 inch. Plan one snail per 5–10 gallons, starting at 5 gallons. They graze algae and biofilm, lay eggs that do not hatch in freshwater, and need a lid.
Min. tank: 5 gal
Care notes →
Freshwater · Beginner
Mystery snail
Pomacea diffusa
Mystery snails (Pomacea diffusa) are the gold, ivory, blue, and magenta apple snails sold for aquariums. Same care across those color morphs. Adults reach about 2 inches. Plan 5–10 gallons for one, and expect more bioload than a nerite. They breathe at the surface, lay pink clutches above the waterline, and will tour the carpet if you skip the lid. Hard water and calcium keep the shell intact.
Min. tank: 5 gal
Care notes →
Freshwater · Beginner
Guppy
Poecilia reticulata
Guppies are colorful, active livebearers for a heated 10-gallon (or larger) community, with one caveat: mixed sexes will produce fry, often lots of them.
Min. tank: 10 gal
Care notes →
Freshwater · Beginner
Endler's livebearer
Poecilia wingei
Endler's livebearers (Poecilia wingei) are about one-inch males (females a bit larger) for a heated 10-gallon colony. Hard, alkaline water, gentle filtration, and micro foods. Mixed sexes mean fry. Keep them apart from fancy guppies if you care about strain purity.
Min. tank: 10 gal
Care notes →
Freshwater · Beginner
Platy
Xiphophorus maculatus
Platies are hardy, hard-water livebearers for a heated 15-gallon (20 is easier). Mickey Mouse, wagtail, and sunset are color strains, not different care. Mixed sexes mean fry.
Min. tank: 15 gal
Care notes →
Freshwater · Beginner
Molly
Poecilia sphenops
Common mollies (Poecilia sphenops) are hardy, hard-water livebearers for a heated 20-gallon. Sailfins want 30+. Mixed sexes mean fry. Captive-bred stock lives in freshwater. They need minerals, not a permanent NaCl bath.
Min. tank: 20 gal
Care notes →
Freshwater · Beginner
Swordtail
Xiphophorus hellerii
Swordtails (Xiphophorus hellerii) are hard-water livebearers that want swimming length. Plan about 29–30 gallons for a mixed group with one male. Males grow a caudal sword; they hybridize with platies if you mix them.
Min. tank: 29 gal
Care notes →
Freshwater · Intermediate
Goldfish
Carassius auratus
Goldfish are coldwater carp, not bowl ornaments. Fancy strains need tens of gallons and strong filtration; single-tail commons belong in very large tanks or ponds.
Min. tank: 30 gal
Care notes →
Freshwater · Intermediate
Angelfish
Pterophyllum scalare
Freshwater angelfish are tall Amazonian cichlids. They need height more than a long, low tank. About 30 gallons and 18+ inches of height for a pair is an indoor start.
Min. tank: 30 gal
Care notes →
Freshwater · Beginner
Bolivian ram
Mikrogeophagus altispinosus
Bolivian rams (Mikrogeophagus altispinosus) are dwarf cichlids that grow to about 3 inches. One or a pair is comfortable in a 29-gallon or a 40 breeder, and a 20-gallon long works for one or a pair if the rest of the stocking stays light. Keep them at 73 to 79°F on fine sand, with gentle flow, some cover, and a school of small fish to make them feel safe.
Min. tank: 29 gal
Care notes →
Freshwater · Intermediate
Pea puffer
Carinotetraodon travancoricus
Pea puffers (Carinotetraodon travancoricus) are freshwater puffers from southwest India that top out around an inch. One fits a heavily planted 10-gallon. A small group needs a 20 long or larger with plenty of plants. Keep them at 74 to 80°F on frozen foods and snails, in a tank with no shrimp or long-finned fish.
Min. tank: 10 gal
Care notes →
Freshwater · Beginner
Siamese algae eater
Crossocheilus oblongus
Siamese algae eaters (Crossocheilus oblongus) are stream barbs from Southeast Asia that grow to about 6 inches. One needs a 30-gallon tank with 30 inches of length, and a group of three needs a 40 breeder or a 55. Keep them at 75 to 79°F under a tight lid. Young ones eat black beard algae. Adults eat mostly fish food.
Min. tank: 30 gal
Care notes →
Freshwater · Beginner
Peppered cory
Corydoras paleatus
Peppered corydoras are social, sandy-bottom catfish. Keep a group of six or more in a 20-gallon tank with sand, not gravel that can nick their barbels.
Min. tank: 20 gal
Care notes →
Freshwater · Beginner
Pygmy cory
Corydoras pygmaeus
Pygmy corydoras (Corydoras pygmaeus) are one-inch catfish that school in midwater as often as they sift the bottom. Keep eight or more in a cycled 10-gallon or larger with fine sand, gentle flow, and food small enough for their mouths.
Min. tank: 10 gal
Care notes →
Freshwater · Beginner
Bristlenose pleco
Ancistrus spp.
Bristlenose plecos (Ancistrus) stay about 4–6 inches. A 20-gallon long is the floor for one adult; 29–30 gallons is the comfortable home. They need driftwood and wafers. They are not a common pleco and not a janitor.
Min. tank: 20 gal
Care notes →
Freshwater · Intermediate
Otocinclus
Otocinclus spp.
Otocinclus (Otocinclus spp., often O. vittatus in the trade mix) stay about 1.5–2 inches. A school of 6+ belongs in a 20-gallon that has been running months with algae and biofilm, not a new 10-gallon sucker hire.
Min. tank: 20 gal
Care notes →
Freshwater · Beginner
Kuhli loach
Pangio spp.
Kuhli loaches (Pangio spp., usually a trade mix of P. kuhlii and P. semicincta) are banded, eel-shaped bottom fish. Adults reach 3–4 inches. Plan a group of 6+ in a 20-gallon on sand, with a lid and a sponge-safe intake.
Min. tank: 20 gal
Care notes →
Freshwater · Beginner
White cloud mountain minnow
Tanichthys albonubes
White cloud mountain minnows (Tanichthys albonubes) are small, hardy coolwater schoolers. Adults reach about 1.5 inches. Plan a group of 6+ in a 10–20 gallon. Best color and lifespan around 64–72°F, often without a heater in a cool room.
Min. tank: 10 gal
Care notes →
Freshwater · Advanced
Oscar
Astronotus ocellatus
Oscars are large, messy cichlids for dedicated tanks. One adult needs about 75 gallons as a minimum, powerful filtration, and an owner ready for digging, waste, and a long-lived pet.
Min. tank: 75 gal
Care notes →
Freshwater · Beginner
Zebra danio
Danio rerio
Zebra danios are hardy, fast-swimming beginners that want a school of six or more. Ten gallons is a tight floor. A 20-gallon long gives them the horizontal lane they actually use.
Min. tank: 10 gal
Care notes →Related guides
husbandry
How to cycle a fish tank (fishless method)
A fishless cycle usually takes 2–6 weeks. You are done when a 2–4 ppm ammonia dose reads 0 ammonia and 0 nitrite within about 24 hours and nitrate is present, not when a calendar or a bottle says so.
Read guide →
setup
Beginner freshwater aquarium setup
A heated, filtered 20-gallon tank is a kinder first aquarium than a tiny kit. Cycle before you add fish, test your water, and stock slowly.
Read guide →
setup
Low-tech planted aquarium for beginners
A cycled 10–20 gallon, inert gravel or sand, root tabs under crypts, and epiphytes tied to wood, with 6–8 hours of light on a timer. No pressurized CO2 required.
Read guide →
setup
Aquarium sand vs gravel
Gravel for easy siphoning and visible debris. Fine aquarium sand for cories, kuhlis, and other diggers. Either works for low-tech plants with root tabs. Skip play sand and blasting sand.
Read guide →
stocking
Stocking a 20-gallon tank
20 gallon long stocking ideas that work: a midwater school plus bottom dwellers on sand, a livebearer group, or a betta centerpiece. Prefer the long footprint. Cycle first. Skip inch-per-gallon.
Read guide →
stocking
Stocking a 10-gallon tank
A 10-gallon tank fits one honest lane: a betta, a shrimp colony, or a small school. Not a stuffed community. Cycle first, heat with about 50W, and skip inch-per-gallon.
Read guide →
stocking
Stocking a 5-gallon tank
A 5-gallon tank holds one betta, or a colony of cherry shrimp, or a single snail. It does not hold a school. Here is what fits, what to skip, and the gear that keeps a small tank steady.
Read guide →
stocking
Stocking a 29-gallon tank
A 29 is the next honest step after a 20. Inch-per-gallon is still a myth. Pick one community plan: honey gourami centerpiece, hard-water livebearers, or a single adult bristlenose with a midwater school.
Read guide →
stocking
Betta tank mates
Many male bettas do best alone in a heated, filtered 5–10+. Community is a maybe: snails, a calm 20-gallon school, or a female sorority if you accept the risk. Watch for flaring and fin nipping.
Read guide →
husbandry
How to do a fish tank water change
A typical community tank wants 25–30% new water each week, gravel-vac'd and temperature-matched. Nitrates under about 20 ppm is the check, not a calendar.
Read guide →
husbandry
How to treat ich: cure white spot in freshwater fish
To treat ich, also called white spot disease, test the water, pull the carbon out of the filter, and dose one malachite-green or formalin ich medication for your real gallon count. Raise the heat into the upper 70s to low 80s F only if your fish can take it, and add air when you do. Keep treating for several days after the last white spot is gone, or it comes back.
Read guide →
husbandry
How to treat fin rot in freshwater fish
Ragged, shrinking, sometimes white-edged fins. Test first. Ammonia, nitrite, or filthy gravel usually starts it. Fix water, stop nipping, then medicate only if the infection is still advancing.
Read guide →
husbandry
How to quarantine new fish
A bare-bottom 10–20 gallon with a seeded sponge, heater, and lid. Observe two to four weeks, acclimate properly, and treat only when you see a problem, not a medication cocktail on day one.
Read guide →
husbandry
How to quarantine aquarium plants
Keep bladder snails, planaria, and hydra out of shrimp tanks and clean scapes. Dip tough plants in dilute bleach or alum, skip the harsh dip on moss and fine stems, and observe in a separate tub before they share water with the display.
Read guide →
husbandry
Cloudy aquarium water: bloom, dust, or algae
Milky new-tank bloom, scaping dust, green water, and surface film look similar until you test. Ammonia or nitrite up means protect the fish with a change; clear nitrogen with a bacterial bloom means wait.
Read guide →
husbandry
Aquarium algae: what it is and what actually works
Brown diatoms, green spot on glass, hair and thread algae, and black beard are surface problems. Fix photoperiod, feeding, and water changes first. Livestock comes after those levers, never instead.
Read guide →
husbandry
Siamese algae eater vs Chinese algae eater
A true Siamese algae eater has a clean black stripe that runs all the way into the tail fork, tops out around 6 inches, and keeps grazing as an adult. A Chinese algae eater has a sucker mouth, reaches 10 to 11 inches, and often quits algae for the slime coat on slow tankmates. Check the stripe and the mouth before the fish goes home.
Read guide →
husbandry
GH, KH, and pH in the aquarium
GH is calcium and magnesium. KH is the carbonate buffer that stops pH from crashing overnight. Match fish to your tap; do not acid-dose a molly tank toward Amazon numbers.
Read guide →
husbandry
How much to feed aquarium fish
Most community fish need a small pinch they finish in about two minutes, once or twice a day. Leftovers become ammonia. Bettas often want one small daily meal. Goldfish and oscars do better on frequent small feeds than one big dump.
Read guide →
husbandry
New tank syndrome: what to do when fish are dying in a new tank
Fish dying in the first few weeks usually means ammonia or nitrite from a tank that has not cycled yet. Test today. At 0.25 ppm or more of either, change water, feed less, and test daily until both hold at 0.
Read guide →
husbandry
How to acclimate new fish
Float the closed bag for 15 to 20 minutes with the tank light off. Most community fish can then be netted straight in. Drip shrimp, saltwater fish, and anything from water much softer or harder than yours over 45 to 60 minutes. The bag water never goes in the tank.
Read guide →
husbandry
How to lower nitrates in a freshwater aquarium
Keep nitrate under 20 to 40 ppm. A water change is the fastest fix, and a 50% change cuts the reading roughly in half. Then test your tap water, feed less, vacuum the gravel, add fast plants, and check your stocking.
Read guide →
husbandry
How to raise water hardness in a fish tank
Test GH and KH first so you know which one is low. Crushed coral in the filter raises both slowly, cuttlebone feeds snail shells, a remineralizer rebuilds RO water, and a small baking soda dose adds KH. Go up no more than about 2 degrees a day.
Read guide →
stocking
Neon tetra vs cardinal tetra
Check the belly. On a cardinal tetra the red runs from the head to the tail. On a neon it covers only the back half. Cardinals also grow a little bigger, want warmer and softer water, need a 20-gallon for their school, and are mostly wild-caught. Neons are farm-bred, cheaper, and fine in a cooler 10 or 20.
Read guide →
stocking
Stocking a 40-gallon breeder tank
A 40 breeder is 36 by 18 inches of floor, which makes it the best tank for bottom fish at its price. Three stocking plans that pass the calculator: a Bolivian ram pair over cardinals and cories, a pearl gourami trio with harlequins and kuhlis, or a hard-water swordtail and platy tank.
Read guide →
stocking
Endler vs guppy
A male Endler is about an inch long, with a slim body, a short tail, and often a black bar or spot in the middle of the flank. A male guppy is half again as big and usually carries a much larger tail. Both want the same hard, warm water, and they crossbreed, so keep them in separate tanks if you want pure fish of either kind.
Read guide →
stocking
Stocking a 55-gallon tank
A 55 is 48 inches long, about 13 inches front to back, and 21 inches tall. That height suits angelfish and the length suits fast swimmers, but the narrow floor leaves less room for fish that hold territory. Three plans that pass the calculator, with fish counts, filter and heater sizes.
Read guide →
husbandry
How to get rid of pest snails
Bladder, ramshorn, and Malaysian trumpet snails come in on plants and multiply on leftover food. Feed less first, then trap them overnight and pick them off by hand. Assassin snails help over a few months. Copper snail killers also kill shrimp and the snails you wanted.
Read guide →