Quarantine: the calm starts before introduction day
The introduction most likely to stay calm is the one where the new fish is already known to be healthy. A simple separate tank — even a modest setup with a heater, a small filter and a hide — holding new arrivals for a couple of weeks lets you watch them eat, breathe and behave before they ever meet your residents, and any illness shows up where it can be dealt with alone. Fish that skip quarantine and sicken in the main tank create the worst introductions of all: catching, rearranging, stress on every fish at once. If you genuinely have no second tank, buy from a shop whose tanks you trust, choose fish that are feeding eagerly in the shop, and accept that your introduction day needs the slow, careful version of everything below.
Reset the territory map
Established fish own places: the cave, the corner under the filter, the exact patch of sand. A newcomer blundering into owned ground gets chased not from malice but from property law. An hour before the new fish go in, rearrange several pieces of decor — move the cave, shift the wood, swap two plant positions. You are not redecorating; you are dissolving the map. Residents now have exploring to do, old boundaries no longer match the layout, and the newcomers arrive in a tank where every fish is equally slightly unsettled, which is a far fairer start than being the only stranger in a settled neighbourhood.
Introduction day, hour by hour
Feed the residents a good meal first — hungry fish investigate newcomers as food-shaped rivals; fed fish investigate them as scenery. Acclimate the new fish slowly by floating and mixing tank water, then net them in with the lights low or off. The first hour is the one to watch, from a chair rather than hovering. Expect inspections: a resident following a newcomer, a brief flare or display, short chases that end when the new fish reaches cover. That is sorting, and it fades. What should not fade — one fish driven from every hiding place, nipped fins appearing, a newcomer pinned in a top corner — means the pairing itself needs intervention, not more time.
The first week's social weather
Keep the lights on their normal schedule from day two, feed a little at both ends of the tank so nobody has to cross a rival to eat, and resist adding anything else — no extra fish, no major rescape — while the hierarchy sets. Most community combinations settle within days into a working arrangement you can read at feeding time: everyone eats, everyone has a resting place, chases are rare and brief. Note which fish rests where; a newcomer still sleeping in a different spot every night has not yet been given a home by the group, and a spare cave placed near its current refuge often finishes the negotiation.
If one fish gets singled out
Persistent targeting is a stocking fact, not a patience test. Move the bullied fish to the quarantine tank to recover, then decide honestly: some combinations — a territorial male with a similar-looking rival, fin-nippers with a long-finned tankmate — do not mellow. Rehoming one side of the mismatch, or returning the new fish to the shop while it is still healthy, is a better outcome than weeks of hiding and torn fins. So the whole household reads the situation the same way, agree who feeds, who watches and who tops up that week while the tank finds its balance. Before that first tank week ends, a relative you pick can open its profile through KinsLe Family Sharing.