Why the chemistry gap matters more than the temperature
The water in a shop bag and the water in your tank differ in more than warmth. pH, hardness and the waste that has built up during the journey all sit at different levels, and a fish tipped straight from one into the other has to adjust its whole internal chemistry in seconds — the shock owners blame when a new fish is lost overnight is very often this moment. Acclimation is simply stretching that adjustment over half an hour or more, so the fish's body changes gear gradually. Temperature still matters — a cold bag needs floating in a warm tank — but it is the slow mixing that does the real protective work.
Floating and mixing, step by step
Start by floating the sealed bag in the tank, out of the brightest light, for around twenty minutes, until the water inside matches the tank's temperature. Open the bag, roll the top down so it floats like a collar, and add a small cup of tank water. Wait five minutes or so and repeat, in small additions, until the volume in the bag has at least doubled — sensitive species and fish that have travelled far deserve the slower end of this, up to an hour of gradual mixing. A drip line from the tank does the same job hands-free for particularly delicate arrivals. While you wait, the bag stays in the tank so the temperature you equalised does not drift again.
Net them in, keep the bag water out
When the bag holds mostly your water, lift each fish out gently with a soft net and release it into the tank. The remaining bag water goes down the sink, not into the aquarium: it carries the ammonia the fish produced in transit and whatever the shop's system water held, and there is no reason to import either. If a fish arrives looking stressed — lying on its side in the bag, gasping — shorten the float, prioritise getting it into clean, oxygenated tank water sooner, and give it darkness and quiet rather than a long ceremony. Most healthy fish, though, come through the standard mixing unbothered and start exploring within the hour.
The first evening and first week
Dim or switch off the tank lights for the rest of the arrival day. Residents do their investigating by sight, and low light turns introductions into brief inspections instead of chases; new fish also find cover faster in a dim tank. Hold off feeding until the next day — an unsettled fish rarely eats, and uneaten food only loads a filter that is about to meet extra waste anyway. Over the first week, test the water a few times, because new mouths mean new waste and a small ammonia bump is common; small water changes keep it in check while the filter catches up. Watch at feeding time once normal meals resume: the newcomer eating in the open is the clearest sign the acclimation has fully taken. New arrivals settle best when nobody has to remember the whole sequence alone: on KinsLe, Care Teams lets you hand the float, the mixing rounds and the first week's testing schedule to whoever is helping, with a timestamp on each completed step so nothing in the routine gets skipped or doubled.