The guide's reader is not a fishkeeper. It is a kind neighbour standing in your hallway, phone torch on, looking at a silent filter. One page works only if it assumes nothing: no jargon, no judgement calls, no branching choices. Everything on it should be observable at a glance or doable in one action, and everything genuinely complicated should route to a phone number, not a paragraph.
Lead with what normal looks like
Open with three sights and sounds the sitter can verify in ten seconds: the filter humming or water moving at the outlet, the thermometer reading in the band you write down in plain numbers, and fish spread around the tank rather than crowded at the surface. Add one line on feeding — where the pre-measured pots are and that one pot is a full day. A sitter who can confirm "normal" confidently will not invent problems, and will spot a real one faster.
Script the four failures worth acting on
Almost every holiday emergency is one of four. Filter stopped: check the plug and the switch, and if it stays silent, leave it — a few quiet hours harm less than a panicked strip-down — and call the shop number. Heater fault: if the water feels much warmer or colder than usual and the reading is outside the band you wrote, switch the heater off at the wall for heat, or wrap the tank in a blanket for cold, then call. Leak: towels down, electrics off if water is near sockets, fish left in the tank unless water is dropping fast. Power cut: lid closed, no feeding, no opening to "check the oxygen" — stillness conserves it.
Write the don'ts as firmly as the dos
Sitters cause damage by trying hard. Your page should forbid, in friendly capitals if needed: no water changes beyond the single emergency step you have scripted, no medication or chemicals from your cupboard however convincing the bottle looks, no extra food for a fish that "seems hungry", and no unplugging or re-plugging equipment in new combinations. Each don't protects the fish from a well-meant mistake you cannot undo from a beach.
Test the page before you trust it
Walk your sitter to the tank with the page in their hand and let them talk you through a pretend filter failure. You will hear the ambiguous sentence — everyone writes one — and fix it in a minute. Stick the final page on the tank or the fridge, not in a drawer, and leave a marker pen beside it so the sitter can note the time anything happened. Those notes are gold when you get home.
If a problem does arise, the page tells your sitter what to do first — and KinsLe Messenger gives them where to say it: every conversation about your tank sits in one per-pet hub, so the sitter's message, your reply and the shop's advice stay in a single thread you can pick up the moment you have signal.