Okay,one,how large are you planning for the next tank to be?And how much experience do you have with saltwater?I would reccomend 1-2 years before trying sharks,because they are not forgiving species.By no means am i trying to burst your bubble,but port jacksons and zebra bullheads need tanks over 3000 gallons.And zebra bullheads are almost unheard of.If you really like bullheads,go with horn sharks.They need tanks of 300 gallons though and need temps from 54-68 degrees,requiring good chiller.But before anyone cn answer fully,what size tank would you move them into?