Also test the change water to be exactly the same as the baby growout tank's (pH, salinity & temp. mainly). At this stage, they're very sensitive to changes in the water composition & being extra careful will hopefully pay off.
Not to be a downer, but if it doesn't work out, don't be too discouraged because most breeders (whether for seahorses or other species) are unsuccessful with their first batch of young. Good luck with this "new pile of extra work you weren't expecting"
Anthony