Another idea is to get a book or website(depending on what sources you are allowed to use) that is an authority on betta care. For persuasion you can use emotion to draw the reader, but it helps to back up your claims with evidence. So prove they ARE sick, and then make them feel bad about it, LOL!
And you can call me anything you like as long as I know you're talking to me. I've been called purple, muffin, muff, etc. whatever. Or you can call me Kat!