I started both my dragonets in a 29g biocube. I fed severla times a day with the flow off and with a turkey baster to target feed. I tried maybe 15 different foods and it seems they both like cyclopeeze at first and then worked their way up eating larger sized foods. It took about a month to train each one and now they eat all the frozen food I put in the tank and the mandarin even eats pellets that fall to the sand.
I did however have a large pod population when i started which is good cause they both would have died of starvation if I hadn't. :-(
Just throwing some pods
in and then a mandarin isnt usually enough. You really need the pods
to develop on their own and to stablize their population before adding the dragonet. Now that it has a sunken tummy the odds arent in your favor for it to make it. :-( I know it;s horrible and all but its a specialty fish and really really needs a lot of work put in for them to thrive.