O's are a tough and hardy fish but very temperamental and intelligent as stated before your O will more then likely eat the rest of your current stock before they have a chance to grow up. Oscars grow very fast so start thinking about a new tank 75 gallons+ for him to live in permanently. As you've already found out they will eat anything that fits in their mouth so choose tankmates carefully. Oscars are pigs and will bring your bioload way up so you're going to want to over filter and keep up with water changes or your tank will fall quickly into disgusting state. For the most part they will tolerate a wide range of water parameters as long as the water is clean, they will also tolerate temps from 75-85*F 79-82* are preferred though. All in all they a re fairly simple to care for and far from picky the only thing an O needs apart from other fish is space beyond that no real special attention is needed, they are very personable and have interesting and varying personality's Im sure you grow to love your evil little O