Keep the log for ember tetras, and let it be a colour and behaviour log, because that is where this species keeps its records. An ember tetra is one of the smallest tetras in the hobby, a translucent ember-orange fish that schools in the middle of the tank, and weighing one would be both impractical and unkind. Fortunately, a healthy ember advertises its condition constantly: the orange deepens, the body looks plump and glassy rather than pinched, and the school drifts and turns together. Your job is simply to write down what you see, regularly enough that slow changes become visible.
Colour first, because embers report through it
Note colour in plain words at a fixed point in the day, ideally at the morning feed under full light. Embers pale overnight and when startled, so comparing a just-lit tank with yesterday's evening colour produces false alarms and false reassurance alike. A school that is steadily deepening in colour over its first month is settling well. A school that was rich orange and has gone watery over a week is reporting something: water that needs testing, a diet that has narrowed to one flake, or bullying from a larger tankmate that keeps them pressed into the plants.
Log new fish separately at first. Shop embers are frequently pale, empty-bellied youngsters, and the log should show them gaining body and colour week by week. A newcomer who is not visibly filling out after two weeks of feeding while its tankmates thrive deserves its own line, and closer watching at feeding to confirm it is actually swallowing food rather than being shouldered aside.
Schooling and appetite entries
Count the school weekly and note the count. In a thicket of plants an ember can die unnoticed, and the count is how you catch it before water quality pays for it. Note cohesion too: embers that have spread out singly through the plants, rather than holding a loose school, are often responding to a predator-shaped tankmate, a current that is too strong for fish of their size, or water that has slipped. Note who feeds. In a school of fifteen, one fish consistently missing the feed is invisible unless the log makes you look for it.
Pair every health entry with the basics from the same day: temperature, whether a water change happened, and any new fish, plants, or foods. Ember problems are usually environmental, and the entry that pairs fading colour with the week the filter was replaced explains itself when you reread it later.
When entries should trigger action
Take the log to an aquatic veterinarian or experienced aquatics shop promptly if several embers develop white spots or a velvety sheen, if fins clamp and breathing quickens across the school, or if deaths begin. One fish wasting while the school thrives, despite confirmed feeding, is also worth advice rather than another week of notes. Bring the log; for fish too small to examine easily, the history of colour, appetite, and water that you have written is most of what an expert has to work with, and it is genuinely useful.
A minute or two a week keeps this record honest. KinsLe's Pet Passport stores this ember school's health notes with its other records together, so anyone caring for the tank reads the same history.