Re the Petsmart employee's advice, i have 3 tanks that prove he's wrong. My 75 gallon is a well planted mixed community of livebearers, tetras, rasboras and danios. I have three female bettas and I just added 1 male betta to the mix. Up until recently I had a different male, but he was shy and stayed in his man cave, so I moved him. The new guy is more outgoing and is doing fine. I have a 15 gallon that houses 7 glofish danios and one male betta. They get along beautifully. And I have one male orange butterfly who lived in a 20 long with 2 gouramis and they were fine. I have him in a divided 10 gallon. For quite a while he also had a visible neighbor in a nano next door. When I moved his neighbor he became visibly depressed. When I got him another neighbor he cheered up and was his happy self again. I have concluded that I have to keep him in a setting with neighbors.