Fish Care

Fish care is the part of the hobby where generic advice stops being useful. A betta and a corydoras and an apistogramma are all “freshwater community fish” on a shop label, but they come from different continents, eat different food, prefer different water, and behave so differently that the same tank cannot keep all three happy. The guides in this section break care down by species and by group — because that is the level of detail fish actually need to thrive, rather than merely survive.

Three things make the difference between a fish that lives for two months and a fish that lives for five years. First, adult size: the juvenile in the shop is not the fish you are buying. The 4 cm oscar becomes a 30 cm predator; the 3 cm common pleco becomes a 45 cm waste machine. Every guide here lists the adult size, the growth rate, and the tank size that adult actually requires — not the tank size it can technically survive in. Second, water parameters: a discus at pH 6.5 and a livebearer at pH 8 are not interchangeable, no matter how hard the pet shop tries to sell them as community fish. Third, social behaviour: schooling fish kept alone develop stereotypies (repetitive swimming, refusal to feed); solitary territorial fish crammed with conspecifics will fight to the death.

The single most useful habit you can build — before you ever buy a fish — is to look it up on at least two independent sources and check three numbers: adult size, pH range, and temperature range. If your tap water is pH 7.8 and the fish needs pH 6.0, you either commit to RO water for the life of the fish or you choose a different fish. The Research Before You Buy guide walks through this in detail; the species guides below assume you have read it.

Stocking is where fish care gets political. Every aquarist has an opinion on the “one inch per gallon” rule, and every aquarist who has kept fish for more than a year knows it is wrong. It ignores body shape (a 4-inch deep-bodied oscar produces ten times the waste of a 4-inch slim-bodied tetra), it ignores filtration capacity, and it ignores social needs. The real limits are bio-load (can your filter process the ammonia?), territory (does every fish have enough space to call its own?), and behaviour (will these species coexist without stress?). Our nano fish stocking combinations guide gives worked examples at common tank sizes; the stocking calculator does the arithmetic.

If you are starting with a small tank (under 20 gallons), the species section matters even more. Small tanks narrow your options dramatically — a 10-gallon tank cannot ethically house goldfish, common plecos, oscars, or any fish that grows larger than 7 cm. The best fish for a 10-gallon tank guide lists every species that genuinely works at that size, with group sizes and sex ratios. The best nano fish guide does the same for tanks from 5 to 20 gallons. The 10-gallon hub is the central reference for everything you can do at that tank size.

Cichlids deserve their own sub-section because they break every community-tank rule. Dwarf cichlids (apistogramma, rams) can coexist with tetras in a planted tank; new-world cichlids (convicts, firemouths) need species-only setups; African rift-lake cichlids need hard alkaline water and overcrowding to suppress aggression. The nano cichlid hub covers the dwarf species that fit in 20–30 gallon tanks; the apistogramma and ram guides go species-deep on the two most popular dwarf cichlids in the hobby.

Bottom dwellers are the most underrated fish in the hobby. Corydoras, loaches, and bristlenose plecos are not “clean-up crew” — they are active, social, long-lived fish that need their own care plan. The corydoras guide covers group size, substrate, and the temperature compromise that lets corydoras live with tropical tankmates without shortening their lifespan.

Finally, the betta. The single most-kept fish in the hobby, and the most-kept-wrong. A betta in a 1-gallon vase is animal cruelty dressed up as decor; a betta in a heated, filtered 5-gallon tank is a territorial, intelligent, long-lived fish that recognises its keeper. The betta care guide covers tank size, water parameters, feeding, tankmate compatibility, and the health problems that almost always trace back to poor water quality rather than bad luck.

How to use this section

Read the guides for the fish you already keep first — you will almost certainly discover that one of your assumptions about them was wrong. Then read the guides for the fish you are considering before you next visit a shop. The cold-water nano fish guide is worth reading even if you have a tropical tank, because it explains why “cold-water” does not mean “unheated room temperature” and which “tropical” fish are actually subtropical and suffer at 27°C.

Pair every species guide with the Stocking Calculator — it converts your tank dimensions to true water volume (after substrate and decorations) and tells you how many of each species you can keep. The Nano Stocking Wizard goes further for small tanks, suggesting complete compatible combinations rather than just counting fish. The Nano Cichlid Stocking Calculator does the same specifically for dwarf cichlid setups.

One warning before you go deeper: most species-specific advice online is recycled. The same five sentences appear on fifty websites because they were copied from the same 2008 forum post. These guides are written from working-tank experience and updated when the advice turns out to be wrong — which it sometimes does. Trust the fish in your tank over the article on the page.