The two rules behind every neon tetra pairing
A neon tetra is a small, soft-water schooling fish that barely reaches an inch and a half, which makes its compatibility rules simple. First, size: a neon fits in the mouth of more fish than new keepers expect, and a tank mate that cannot eat it today may manage it after a year of growth. Second, temperament: neons are easily stressed, and a single chasing or fin-nipping fish turns a confident, glowing school into a group hiding behind the filter. Judge every candidate by its adult size and its adult behaviour, not by how small and harmless it looks in the shop tank.
Tank mates that suit neon tetras
Fish of similar size and calm habits are the reliable matches. Cardinal tetras and green neon tetras school alongside neons and share their preference for soft, slightly acidic water. Chili rasboras and other tiny rasboras occupy the upper water without any interest in the school. On the bottom, corydoras of the smaller species and otocinclus catfish graze and sift without ever troubling the tetras, and they use space the neons leave empty. A honey gourami makes a peaceful centrepiece, and cherry shrimp are generally ignored, though their smallest babies may be picked off. Hatchetfish add life at the very surface, provided the tank has a tight lid, since they jump.
Fish to keep away from the school
The famous trap is the angelfish: bought small and angelic, it grows into a cichlid that hunts tetras at night, and neons are its natural prey in the wild. Larger cichlids, bigger barbs, and most fish sold as community centrepieces with a wide mouth belong on the same list. Fin-nippers such as tiger barbs and serpae tetras will not eat a neon but will harass the school ragged. Bettas are a gamble by individual: many ignore neons, but some chase them, and the tetra's bright colours seem to provoke certain males. Goldfish are unsuitable twice over, needing cooler water and growing large enough to swallow a neon whole.
Keeping the school itself strong
Tank mates matter less if the school is too small to feel safe. Keep ten or more neons so they hold a loose, confident formation in open water instead of scattering. Planted cover at the back and sides, a darker substrate, and gentle filtration flow all help their colours stay at their brightest, since a pale neon is usually a stressed neon. Add tank mates gradually, and add the neons last where you can, so the smallest fish are not trying to settle while larger strangers rearrange the tank around them.
Checking a pairing before it happens
Most neon losses come from one unresearched addition, so it pays to check adult size and temperament before a bag is opened. Before any bag is opened in the shop, put a follow-up question to KinsLe's Kimmy; she answers using the KinsLe Answers library.