I have hears undergravel filters aren't the best, but that's on a side note. I have many orandas. The question for you is how big is the oranda? If you want him to reach his or her maximum size of course a ten gallon is too small. I have about ten fancy goldies in a 75 gallon two of which are 6 years old black moors . At 6 years old they are pretty big. So if you want to make him more happy and most of all more healthy I would upgrade your tank to atleast a twenty gallon and if you add anymore make it only common golds for color to the tank don't add any fancy until you have a bigger tank than twenty... Weekly water changes are recommended also for goldies. They are quite dirty