Why one tank of siblings stops being fair
Goldfish fry from a single spawning do not grow as a matched set. Within a fortnight the batch usually contains a few shooting ahead, a broad middle, and a tail of runts a fraction of their siblings' size — and the differences feed themselves. Bigger fry reach food first, swim more strongly in the current from the filter, and hold the good positions; smaller fry spend energy avoiding their own brothers and sisters and arrive at meals after the best of them has gone. Left unsorted, the gap widens every week, and in goldfish it has a hard edge: once the largest are big enough, the very smallest stop being competitors and become prey. Grading exists to interrupt that arithmetic while it is still arithmetic, not predation.
Sort gently, over a tray, with the water they live in
Grading day should be the calmest handling these fry get. Fill a shallow white tray or washing-up bowl with water from the fry tank — the pale background makes small, translucent fry visible and countable in a way dark gravel never does. Lift fry a few at a time in a soft, fine mesh net, or better, coax them into a small cup or ladle so they never leave the water, and never chase a fry with a net: exhaustion and scale damage in a fish this size cost more than the sorting gains. Work in short sessions, keep the tray out of direct sun so its shallow water does not warm, and return every fish to a tank of its home water as soon as its group is decided.
Run two or three groups, each with its own water
The sort produces groups, and the groups need somewhere honest to live: the largest fry to the roomiest quarters, since they will need the space first; the middle group in the original nursery tank; the runts in their own smaller tank or a divided section where nothing bigger can reach their food or their tails. A floating breeding trap inside the main tank will do for a few days in an emergency, but it is not a grading home — its water volume is too small for the frequent feeding runts need. What matters is matching opportunity: each group in water whose feeding, flow and crowding suit its size, so the smallest group's rations reach the smallest mouths.
Feed the smallest group like it is the point of the exercise
Grading without a feeding change is just tidier neglect. The runts' group should be fed first at every round, before the big tanks distract you; fed more often, in the small suspended meals their size demands; and watched at the surface to confirm they are eating in the open rather than hiding from the current. Many runts are not weaklings but late starters, and two or three weeks of unguarded food and quiet water brings a surprising number of them back into the middle group at the next sort. At each re-grade, promote the growers, demote anyone being left behind again, and be honest about the few who remain deformed or failing despite good conditions — a decision for you, with your aquatic shop's advice if you need it, and never a reason to keep a suffering fish.
Plan for the numbers grading reveals
Sorting makes a batch's true size impossible to ignore, and goldfish batches are large. As the groups grow, water, filtration and eventual homes all have to be found: rehome healthy fry to other keepers or a shop that takes them, grow on only the number your ponds and tanks can hold as adults, and never release fry to any outside water, whatever the temptation. Record each sort — how many in each group, how the runts are progressing — because that running tally is your stocking plan for the season, not just a diary. Fixing the sort as a recurring duty in KinsLe Care Teams keeps the fortnightly rhythm intact when the batch is at its most demanding, with each grading session's counts noted against the date it was done.