The serpae tetra is a deep red, black-marked characin from the Amazon and Paraguay river systems with a reputation problem - and the reputation is mostly a stocking error. Adults reach an inch and a half to two inches, and in a proper school they are hardy, active, and striking. That school is the condition: plan on eight or more fish, which means a 20-gallon tank at minimum, planted enough to break up sight lines. Kept that way, serpaes are a pleasure; kept in threes, they are the fin-nippers everyone warns you about.
Numbers are the behavior fix
A serpae's urge to nip does not disappear in a big school - it gets redirected. With eight to twelve of their own kind around, serpaes spend their sparring budget on each other in quick, harmless hierarchy games, and tank mates stop being interesting. Shrink the group and the same energy looks for targets: a slow guppy's tail, an angelfish's fins, the weakest serpae itself. This is why serpaes should never be sold or bought as pairs, and why topping the school back up promptly after any loss matters more for this species than for most tetras. Twelve is not excessive - in a 30-gallon it is arguably the ideal, a red crowd that behaves like a single fish. More serpaes, paradoxically, means a calmer tank.
Planting, water, and light
Serpaes come from slow, plant-choked waters, and their tank should feel like it: tall planting at the back and sides, some cover overhead, and an open lane in the middle for the school's patrols. They are adaptable fish across a broad range of ordinary water conditions, warm in the mid-70s Fahrenheit, and their red deepens noticeably in soft, slightly acidic water under subdued light. Under bare bright light they sit lower and look browner than they are. Feed a varied diet with some meaty small foods; condition shows in the depth of red within weeks.
Choose tank mates with short fins
The rule for serpae company is simple: nothing slow with long fins. Bettas, fancy guppies, and angelfish are the classic casualties even in a well-sized school, because a trailing fin at serpae height is an invitation. Fast, short-finned fish do well - other robust tetras, danios, corydoras, and small barbs - and bottom dwellers largely get ignored. A second school of a differently colored tetra at the same level usually works better than one long-finned centerpiece ever will. In a mixed tetra tank, keep the serpae school the biggest personality in the middle layer, or give that role to another species entirely. Watch the first days after any new addition; serpae curiosity is front-loaded and usually fades.
A feeding rota for a tank with several keepers
Serpaes are enthusiastic feeders, and in a household where two people each assume the other has not fed, this school will happily eat twice and foul a 20-gallon fast. Put the job on a list with names attached. KinsLe's Care Teams lets you assign this tank's feeding and water changes to specific people, with each completed task marked by a timestamp, so the school's enthusiasm never turns into double dinners.