The size test that decides it for angelfish
Young angelfish are ready for the main tank when the deep disc of the body is plainly too wide for an adult angelfish to swallow, and fin length does not count in that judgement because trailing fins fold. Adult angelfish have surprisingly large mouths for such graceful fish, and they will eat a juvenile that fits, however peaceful they seemed beforehand. A coin-sized, deep-bodied youngster that has been growing steadily for weeks is a far safer candidate than a smaller, slower sibling from the same spawn. Judge each young angelfish individually rather than moving the whole batch on one date, since angelfish spawns always produce a few runts that need more time in the grow-out tank. If an adult can still line up a youngster head-first and the youngster's body depth looks marginal, wait.
Feeding confidence matters as much as size
A young angelfish joining adults must reach food while taller, faster adults are feeding around it, so only move youngsters that already push forward at meals in the grow-out tank. In the main tank, adult angelfish feed in the upper and middle layers and can strip the water column before a timid juvenile gets a share. Watch the candidates at feeding time: the ready ones rise quickly, take flake or small pellets without hesitation, and keep condition along the belly instead of looking pinched behind the head. A young angelfish that hangs back in its own tank will hang back even further beside adults. Building feeding confidence with varied small foods before the move does more for survival than any acclimation trick on the day itself.
Setting up the introduction so adults accept them
Move young angelfish in a small group rather than singly, because a lone newcomer draws every adult's attention while a group spreads it. Add tall plants, driftwood, or a rearranged corner beforehand so the youngsters have vertical cover that matches how angelfish naturally hold station among stems. Feed the adults well shortly before release, dim bright light if your setup allows it, and float or drip-acclimate the youngsters so temperature and water chemistry match the main tank. Expect some display — flared fins, parallel swimming, and short chases from the resident adult angelfish — but repeated biting, torn fins, or a youngster pinned in a corner means it comes back out to grow on. Late-day introductions often settle fastest because the tank quiets soon after.
The first week after young angelfish move in
During the first week, check that each young angelfish is eating at every feed, spreading food across the tank so adults cannot guard one spot. Watch fin edges daily for nipping damage, especially the long ventral feelers that tankmates sometimes mistake for worms. Keep the grow-out tank running as a fallback rather than emptying it on moving day, since returning one bullied youngster is simple only if its old home still exists. If the youngsters hold their own, school loosely with the adults at times, and keep growing, the move has worked. Noting move dates, sizes, and any fin damage in KinsLe through Care Teams means anyone feeding the tank knows which young angelfish still need a watchful eye.