He's right, if the fish jump out of the tank at night, no one will be there to get them. As said before, they're fish, they don't need you to put air in the tank. Most people do it anyway but it's not really needed. Taking the top off the tank will just make their water get dirty faster and allow them to jump out; nothing good. That being said, if I were you, I'd just use the oxygen generator that you have, it can't really be "too strong" for the fish. As long as they have a heater and a good filter, they'll probably be fine. You can feed them 1-3 times a day, really up to you. Be careful not to feed them too much though. Change the filters and water regularly (whenever it's visibly dirty). Make sure to clean the tank too. If you're wondering, I have 3 fish tanks, so I kinda know a lot about taking care of fish. :P