Teach the sitter your goldfish's ordinary day
Begin the brief at the tank, together, at feeding time. Show the sitter how your goldfish swims its laps, how it sifts the bottom, how it rests, and how enthusiastically it normally feeds, because goldfish emergencies are usually recognised as a departure from a routine the sitter must first have seen. Point out its normal trim in the water, since a sitter who has never watched the fish hover level will not spot the first degree of tipping.
Then walk the life-support rather than the fish: filter running and its normal hum, air supply if fitted, heater where relevant, and the temperature and test readings you consider normal for this tank. Have the sitter run a water test once under your eye so the kit is familiar before it matters.
The emergencies, in the order they kill
For a goldfish, loss of filtration and aeration is the emergency that outranks the rest, because this fish fills its water with waste and draws heavily on its oxygen. Brief the sitter accordingly: if the filter stops or the power fails, the first move is the battery air pump stored beside the tank, fitted exactly as you have shown them. The second move is to stop feeding entirely. The third is to call you. A goldfish can wait safely unfed far longer than it can wait unaerated.
Buoyancy trouble is the second briefing. A goldfish found floating at the surface unable to dive, sunk on the bottom unable to rise, or tipped on its side gets a call to you and to the vet the same hour, not a home remedy and not a handful of any folk cure added to the tank. The sitter's job is observation, aeration, and the phone call; diagnosis belongs to the vet.
A fish found on the floor goes back into tank water immediately with wet hands and you are called at once, whatever state it appears to be in.
What the sitter should never attempt alone
Goldfish invite well-meant disasters, so close the doors explicitly. No large water change without you directing it live, because unmatched water can shock a fish already in trouble. No filter media replaced or rinsed out, since the sitter cannot know which part holds the bacteria the tank depends on. No treatments, salts, or remedies added on a neighbour's advice. No netting and moving the fish to a bucket of fresh water while help is available by phone.
Give written authority to call the vet and to buy a replacement air pump or heater without checking the price with you first. In your absence the sitter is your judgement on the scene, and a brief that makes them afraid to act has failed at its only job.
Leave the kit and the contacts as one package
Store the emergency kit where the brief says it is: battery air pump with fresh batteries, spare tubing and stone, water conditioner, test kit, a torch, and the vet's number, yours, and a fish-keeping backup contact, all in or beside one box by the tank. Label the normal temperature and the daily portion on the brief itself.
Rehearse the power-cut drill once, pump in hand, before you travel. Two minutes of practice converts the likeliest emergency from a crisis into a checklist.
That checklist is most useful when it is in the sitter's hands rather than your outbox, and KinsLe provides it through its Care Pass, giving your sitter temporary, clear access to the goldfish's emergency order, contacts, and daily routine until you return.