I would say you should just move the Oscars, Snake, and Clown up. You will have to remember adult size with these guys. The Oscars will get a foot a piece, the Snakehead will get 2-3 feet, and the Knife will get 3-4 feet. That is a lot of big fish for a small tank (150). I may be a little off on adult size since I have never kept any of the above mentioned fish but know tons of people that do. Plus like PBQ said the gobies and puffers are technically brackish (20% saltwater 80% freshwater) so they should be kept on their own.