LionFish says.......
Well, when it comes down to it, you have to think of it this way. Lionfish, no matter what the variety, get large. And they need a lot of space. I have never personally owned a corner tank, due mostly because I have heating vents in the corners. If you feel the need to keep a lion, you would have to go with a Dwarf Lion. Radittas and Antennatas don't get too much large than Dwarfs. Only an inch or 2. But they have a much larger fin span. I would only recommend a Dwraf Lion in your 54. Seeing as it is a corner tank, I might even consider that to be pushing it. Fritz make that point of less horizontal space which is necessary for them to live and thrive. If you have anymore questions, please ask.