The honest answer for two bettas: two tanks
A second betta needs an entire second setup, not a corner of the first fish's tank. Bettas are territorial, and two males placed together will chase, flare, and bite until one is badly injured. Even two females are not a safe pair on their own, so the working assumption for a second betta is a separate aquarium of the same generous size you gave the first, placed where the two fish cannot spend the day staring at each other through the glass.
That framing matters because owners often price a second betta as a small upgrade. In reality the fish itself is the cheapest part of the decision. The tank, the equipment inside it, and the weekly minutes to maintain it all arrive as a second full set.
Every resource that doubles for the second betta
The second betta needs its own heater, because a shared warm tank is exactly what you are not providing. It needs its own gentle filter, its own light on its own schedule, and a snug lid, since bettas jump and a startled fish in a new home is likelier to try. Inside the glass, plan a second set of soft plants, a smooth hiding cave, and a broad leaf or rest near the surface where this betta can sleep without fighting a current.
Consumables roughly double too. Food portions are small, yet a second betta still means a second feeding routine morning and evening. Water conditioner, test supplies, and replacement filter media are all used twice as fast once two tanks are cycling water changes on the same day.
Space on the shelf, the stand, and the calendar
A second betta claims physical space well beyond the footprint of its tank. Leave working room above the lid for feeding and netting, space behind the tank for heater and filter cords, and a sturdy surface that carries the full weight of filled water, gravel, and decor without flexing. Two tanks squeezed onto a wobbly shelf are a risk neither betta chose.
The calendar space doubles as honestly as the shelf space. Each tank wants its own partial water change, its own glass wipedown, its own plant trim, and its own quick health look each week. Doing both tanks in one session works well, but it is two sessions back to back, and skipping the second betta's tank because the first took longer is how water quality quietly slips.
The one setup that is not a shortcut
A divided tank is sometimes sold as the way to house two bettas in one footprint, and it deserves real caution. A divider that shifts, a fish that slips over the top during a water change, or two bettas that can see and smell each other all day can leave both fish stressed and one of them hurt. If you use a divider at all, it must be opaque, fixed, and tall enough to break the waterline, with separate heating and filtration on each side — at which point you have bought most of a second setup anyway.
Watch a new second betta closely in its first weeks in the separate tank. Faded color, clamped fins, hiding through the day, or refusing food in a betta that was bold in the shop are signs to check temperature, water quality, and current strength, and to ask a veterinarian or experienced aquatic specialist if the fish declines rather than settles.
Keeping two separate betta homes straight is easier when the details live in one place, and KinsLe Family Sharing lets the whole household share each betta's profile and care notes so nobody feeds the wrong tank or repeats a water change the other tank never got.