Measure in flakes the school can finish in a minute
Guppies are overfed when the food outlasts the school's first eager minute, because a guppy's stomach holds very little and fills fast. Crush the flake small, offer a modest pinch, and watch the water column: a right-sized meal disappears while the fish are still dashing for it. Flakes still drifting at two minutes, sinking onto plants, or settling on the substrate to soften are surplus, and in a small guppy tank surplus food decays quickly enough to matter by the next day. Two very small meals suit a guppy's quick metabolism better than one heavy one, and both together should still look like less food than instinct suggests.
Learn the difference between fat males and pregnant females
Body shape misleads guppy keepers more than any other sign, because a female guppy near giving birth looks dramatically full. A gravid female carries her bulk low and rearward, squaring off at the back near the dark gravid spot, and she is supposed to look that way. Overfeeding shows on the males: a male guppy should stay slim and torpedo-shaped, so a rounded pot belly on a male, or a whole group of males plumping together, is the ration confessing. Females that stay swollen long after dropping fry, with no new brood following, deserve the same suspicion. Judge the males and the calendar, and you will rarely misread the tank.
Respect how fast a small tank turns
A guppy colony usually lives in modest water volume, and overfeeding punishes small volumes first. Haze that returns within days of a water change, a white film gathering on the surface, pest snails suddenly multiplying on the surplus, and plants filmed with decaying flake all mean the tank is being asked to process more food than the guppies can. Snails are an especially honest gauge: a snail population that explodes is eating something, and that something is the food your fish left. Cut the ration and the snail boom stalls; keep feeding heavily and no amount of water changing quite catches up.
Watch the fry factor before adding more
Guppies complicate ration-judging because the population itself keeps changing the equation. A tank that was correctly fed last month may hold twice the mouths this month, and fry pick at micro-portions all day among the plants. Resist feeding extra 'for the babies' as a separate habit on top of normal meals — fry find crushed flake and grazing matter within the ordinary ration, and the adults will eat most of any special fry feed anyway, getting fatter on food aimed at their children. Count heads occasionally, and scale the pinch to the colony you actually have rather than the one you bought.
When round is a warning instead of a meal
A guppy that bloats suddenly with scales lifting away from the body, a fish that stops eating and hangs at the surface or hides alone, or several fish going off food together in water that has slipped are not portion puzzles — get the water tested, isolate what you can observe, and seek an aquatic veterinarian's or experienced shop's advice quickly, since small fish decline fast. Ordinary guppy gluttony, though, is a household habit problem: in KinsLe, Care Teams let you log each guppy feed with the amount and a timestamp, so the school's two small meals a day stay two — not one per person who walks past the tank.