It won't last long in a 50 gal. I tried one in a 75, and that one lasted 3 months. If I were you, I would take it back for credit. I would not try one again, unless I had at least a 100 gal, that's been running without problems, for at least 6 months. The fact that you had to ask about it, tells me you aren't ready to care for one. I know very experienced fishkeepers that stay away from keeping the bowder blues/browns, because of the fact they are so ich-prone. Sorry to be the bearer of bad news, but these are VERY difficult fish to keep.
HTH,
B