The Setup Record: the Tank as It Was Built
Start with the tank itself, written down once and corrected whenever it changes: its size and dimensions, the filter and heater it runs, the lights and their schedule, the substrate and the rockwork or planting scheme. Add the water it was started with and how a water change is done in this house — where the water comes from, how it is treated, how it is matched. This page looks dull and gets used constantly: every replacement part, every new fish decision and every troubleshooting question starts from what the system actually is, and nobody remembers their own filter model long after buying it.
Water Tests and Changes: the Running Numbers
The living heart of the log is the run of water tests and changes: each test's readings for temperature, pH, ammonia, nitrite and nitrate, and each change's size and day, in one continuous list. You are not collecting numbers for their own sake; you are building the ability to answer 'when did this start?' — the drift in pH, the creep in nitrate — by looking instead of guessing. Test on a rhythm you will actually keep; a modest set of readings taken reliably beats an ambitious daily scheme abandoned within weeks. When a reading surprises you, write the surprise down beside it, not just the corrected value.
Livestock In, Livestock Out
Keep a population page: every fish, snail and shrimp that arrives — with its source and the day it arrived — and every departure, whether death, rehoming or a move to another tank, with the reason as honestly as you know it. Add new plants and any treatments the tank has had to the same page. Over time this becomes the tank's biography, and it explains things the test numbers cannot: the algae that arrived with a plant, the losses that followed a particular source, the community that has run peacefully for a long stretch. When you add livestock, this page is where you check what the tank has already taught you.
Equipment, Maintenance and Replacements
Give equipment its own short page: what is installed, when each piece was last serviced in your own rhythm — filter media rinsed or replaced, impeller cleaned, heater checked — and what was replaced when something failed. Note the settings that must survive a power cut or a curious toddler: the heater setting, the filter flow position, the light timer's schedule. When a filter dies on a Sunday, this page is the difference between buying the right replacement in one trip and buying the near-enough one that never quite fits. It is also where a sitter's or buyer's questions get answered without a rummage through receipts.
Behaviour and Health Notes in Plain Words
Finally, keep a few lines of observation in ordinary language: how the tank feeds, who hides more than they used to, the snail eggs on the glass, the plant that suddenly thrives. Plain words age better than codes, and these notes are what turn a stack of numbers into knowledge of this particular tank. You do not need daily entries — a line whenever something changes, and a short summary whenever you do a big clean or a rescape, is a rhythm that survives real life. Future you, a sitter, a vet or a buyer will each be glad the lines exist. Records like these are the everyday material of KinsLe's Pet Passport, which keeps each tank's setup, test history and livestock story together in one packet — so the knowledge you have built about your aquarium is never scattered across notebooks and memory.