I feed mine Mussells, shrimp, scallops, squid, vege mixes, Krill, Mysis, and also rockpool critters such as crabs and snails as they need crunchy stuff to eat to keep there teeth down.
Also at 5-6cm 1.010 should be fine, provided that they were either
A) Previously in a tank that was at this SG
B) Have been acclimated to this SG
Over the next couple of days watch the belly colours and tail to give you an indication on there health constantly dark means there COULD be a problem.
What size tank are they in and what sort of filtration are you using.
Also the tank was cycled BEFORE putting the puffers in right?