Hikari sticks are great; at that size, break it half while feeding. Also, try Plankton Freeze dried shrimps. Another option is the Hikari frozen blood worms.
I was in a similar situation and followed the diet mentioned; my Aro is now 7 inches, still loves the Hikari sticks, occassionally eats the plankton; and loves a live feed such as moth or insect from natural surrouding. Guess it does not find the Frozen bloodwroms platable and willnot even approach them.
Good luck.
Fai