I have had much aro experience, some not good of course as part of the laerning curve.
but i have reared monsters as of late.
IMHO - Aros need the 3 commandments.
1) Space - They will need space to grow. swimming space to excercise. Settle it in with little dimmed lights then increase it after a month or two. Should be fine. LIDS!
2) Water quality - Low nitrate, good filtration. not sensitive but always good to have water qual and arowanas eat alot, and digest rapidly... so the amonia will spike if you dont have adequate filtration.
3) food food food! Get them only hikari aro sticks asap. Then after they eat taht comfortably. Not chewing and spitting 50% of the pellet but i mean really eating 80 to 90% of the pellets as you would have a certain degree of fragmentation of pellets when swallowed - THEN SHRIMP.
once aro has shrimp, they love it and its hard to revert them. but a diet of pellets is pretty good.
i hear over seas that silver and balck aro loses its nice sheen because its fed beef heart...turns the scales kinds beige and off white...you want it silver, white in colour with a tinge of pink or in the black aro, bluish....
thsi is achieved by shrimps and pellets like hikari aro sticks. They are expensive but HFF has a awesome sale right now, im getting a KG of aro sticks for 130 ish.
on that note, its funny you buy it with out researching.... interesting approach but hey, as long as you have the means to look after it, thats fine. Remember they grow large.... fast.
1 inch a month is the good target of growth until 12 inches.