Pure superworms even when gutloaded isn't such a great diet. At 20" your aro can easily go for a couple weeks without food. Start starving to get it on shrimp, pellets, etc etc, whatever else you want to feed. Just remember not to stop starving after 2 or 3 days, at that size, even WEEKS isnt a problem.
Like hao said, get the geos out, its basically the only way OR you can get a divider and section off the geos, but either way you still have to seperate them.
starve him then pellets and de-shelled prawn (i find easier to feed market prawn de-shelled and fully de-frosted for the first timers)
They can go long time without food but after couple of weeks you will be itching to give it anything to eat so long as it eats - be strong
PS: my BB (and to lesser extent SR) is also crazy about meal worms (the only food that it never refuses). but BB does eat de-frosted prawn even if not regularly. I find that competition for food is the best incentive (my XB eats like a champ in a comm tank)
PS1: you may want to try hikari floating at the same time ^^
