The first moves, made in the dark
Night changes the order of priorities because the biggest risk in the room is you. Water spreading across a floor in the dark reaches power strips and sockets silently, so your first act is to cut the tank's power — at the breaker if the strip is anywhere near the water — with dry feet and a torch in hand, before you touch the tank at all. Do not walk barefoot through the puddle to reach a plug. Once the electrics are dead, find the drip and judge the leak's height: water stops falling once the level drops below the failure, so you only need to remove enough water to pass that line. A headlamp keeps both hands free for hoses and buckets, which is why one belongs in the kit below.
The night kit that should already live beside the tank
A night leak is won or lost before it happens. Beside or under the stand there should be a siphon hose long enough to reach a bucket, two buckets that are only ever used for the tank, a bundle of old towels, and a torch or headlamp with working batteries. With that kit in arm's reach, the drill is unhurried: start the siphon into a bucket, swap buckets as they fill, and lay towels along the drip path and the floor's low spots. Keep the fish in the tank while you lower the level — they are safest in the big familiar volume until the water stops falling. Families who have talked through who does what, even once, lose far less water to the floor than a solo keeper improvising.
Getting fish and filter safe by torchlight
Once the level is below the leak and the floor is contained, fill one bucket with tank water and move the fish into it, lid or a towel draped over the top so a startled jumper stays in. Lift the filter media into a second bucket of tank water and keep it submerged; the bacteria on it are what make tomorrow's replacement setup survivable for the fish. If the fish will be in buckets for hours, an air stone run from any battery pump helps, and the buckets go somewhere level, dark and quiet — not in a hallway where they will be kicked or investigated by a cat. Do not feed, do not medicate, and do not start repairs on the tank itself in the middle of the night; tonight's job is only containment.
The morning after
In daylight, finish draining the failed tank, photograph the seam or crack, and dry the stand fully before judging whether its boards have swollen or softened. Set up the replacement or repair with the saved media, match temperatures, and return the fish only once the new setup is stable. Then watch them: a fish that feeds normally by the next meal has shrugged the night off, while hiding, clamped fins or rapid breathing that persists means testing the water and taking advice from an aquatic vet if it does not improve. The fastest part of the whole night, in a household that is set up for it, is raising help — and KinsLe Messenger keeps every conversation about that tank in one per-pet hub, so one message wakes the sitter, your partner and your fish-savvy friend together.