It sounds like your fry have been growing fast in developing into good-sized juveniles — congratulations on the successful rearing program!
Of course, before you transfer your juveniles from the nursery tank into your reef system, you’ll want to make sure they are all weaned onto a diet of frozen Mysis.
Other than that, how soon you transfer them into the reef tank depends on how big of an aquarium it is, how powerful the water movement is in your reef system, and whether it houses soft corals or stony corals. The soft corals generally have very weak stings, but the hard corals have more potent nematocysts, and you want to let your juveniles grow a little larger before you introduce them into a tank with SPS corals. Likewise, in large reef systems with strong currents, it’s best to let the juveniles mature and put on a little more growth before they go into your reef tank. Otherwise, small seahorses can sort of get lost in a larger aquarium…
So there are really no set guidelines or time limits regarding when it’s time to move your juveniles from their nurseries into the main tank. However, a lot of breeders prefer to move their juveniles from a nursery tank into a more spacious grow-out tank for a little extra TLC so they can put out a little more size before they go into a their main tank. Depending on what your reef system is like, you might want to transfer your juvies into a grow-out tank next…
Best of luck with your latest crop of youngsters, Seagazer!