My experience has been somewhat different. I have had 2 snowflakes, still have one that is over 2 feet long. He does not eat, nor has he ever offered to eat, any of the tank inhabitants. I feel that this is because he is well-fed and lazy. They do produce alot of waste matter. As far as size of tanks, many people keep them in 55 gallon tanks with success, mine is in a bigger tank. Also, I have not found them to be very active at all unless they are hungry.
Like I said, this has been my experience.