The glowlight tetra is a small, peaceful characin from Guyana's Essequibo River, named for the orange-gold stripe that runs along its flank like a filament. At about an inch and a half as an adult it fits nano setups, and a 10-gallon tank is the accepted minimum for a small group. A 20-gallon is the better home, though - not because the fish needs the water, but because a full school of glowlights holding together in open water is the entire point of keeping them, and small tanks squeeze that school into a corner. Their care is easy once the setting is right.
Built for dim water and dark corners
Glowlights evolved in shaded, tannin-stained streams, and they carry that history into the aquarium. Under bright unshaded light they hug the plants and the stripe fades to a dull line; under softened light, with floating plants overhead and a dark substrate below, the same fish move into the open wearing a stripe that genuinely seems lit from inside. This is a fish whose tank size question is half about gallons and half about gloom - give them shade structures, driftwood, and plant cover, and a modest tank feels twice its size to them. Warm water in the mid-70s Fahrenheit suits them, soft and slightly acidic ideally, though they adapt to a reasonable range.
School size is the welfare issue
Glowlights are obliging community fish but poor minimalists. A pair or trio in a 10-gallon will survive; it will not school, feed confidently, or show color, because this species reads safety from numbers. Eight is a sensible floor for a group, ten or twelve better in a 20-gallon, and the group should arrive together rather than in dribs and drabs. Keep the whole school in the same water layer - glowlights hold the middle of the tank - and avoid boisterous mid-water species that scatter them at every pass. With numbers right, the school drifts and turns as a loose ribbon, which is the behavior the tank exists to show.
Feeding and tank mates
Glowlights take small foods eagerly and are not fussy, but their mouths are small and their manner is gentle, so fast, pushy feeders steal from them. Pair them with other small, calm fish - small tetras and rasboras, corydoras, a peaceful dwarf gourami at the surface - and keep them away from anything large enough to regard a one-inch fish as a snack. Shrimp colonies coexist well once the shrimp are adult-sized. Feed small amounts the school can finish while you watch; in a small tank, leftovers are the quiet cause of most water trouble. A short fast day once a week does the school no harm and mimics lean days in the wild.
Checking before you add anything new
Glowlight tanks drift into trouble by addition - one more pretty species, then another, until the calm is gone. Slow the process down and check each idea against this school's size and temperament first. When a candidate fish comes up for this small, peaceful school, put a follow-up question to KinsLe's Kinny; he answers using the KinsLe Answers library.