First: power off, then find the leak's level
Water conducts, and a leaking tank spreads water toward sockets, power strips and cables. Before you touch anything wet, switch the tank's electrics off at the strip or the wall with dry hands and dry feet. Then look at the waterline: a leak drains the tank only down to the height of the failed seam or crack, so water an inch below the top with a dry line lower down tells you the failure is somewhere between. Knowing that level matters because you only need to remove enough water to get below it, not empty the tank in a panic. Get towels down around the stand, move anything stored underneath, and put buckets where the drip path runs while you work.
Stop the water and rehouse the fish
Siphon tank water into buckets until the level sits safely below the leak point; that stops the loss and buys you unhurried time. Fill a sturdy food-safe storage container or a spare tank with water from the aquarium, move the fish into it, and cover it so jumpers stay in and the water holds its temperature longer. Lift the filter media out and keep it fully submerged in a bucket of the same tank water — the bacteria living on that media are the tank's life support, and they die if the media dries out or sits under tap water. If the holding container has no filter, run an air stone if you have one, and do not feed the fish while they are in temporary quarters; uneaten food fouls a small volume fast.
Protecting the room while you work
Once the fish are safe, finish draining the tank into buckets rather than letting it weep onto the floor for hours. Photograph the damage and the failed seam before you clean up, since clear photos help if you need to talk to the tank's seller about a warranty or to anyone covering water damage to flooring. Dry the stand thoroughly and check it for swollen or softened boards, because a stand that has soaked up water may no longer be trustworthy under a full tank's weight. Keep the fish container somewhere level, out of direct sun and away from pets, with its lid on but not sealed airtight.
Deciding what happens to the tank
A small tank with a failed silicone seam is usually replaced rather than resealed, and any cracked pane means replacement, full stop — do not refill a tank you no longer trust and hope. Set the replacement up with the saved media so the cycle carries over, and return the fish once temperatures match. Watch the fish closely for the next few days: clamped fins, refusal to feed or rapid breathing in a fish that was fine before the leak are signs the stress or a water-quality slip has caught up with it, and that is the point to test the water and seek an aquatic vet's advice if it does not settle. Emergencies like this move faster when nothing has to be remembered under stress, and a KinsLe Pet Passport keeps the tank's stock, sizes and equipment records in one portable packet you can hand to whoever is helping.