They should be fed twice a week to meet their nutritional needs adequately. They naturally grow quite fast. You could very well have more than one in a year or so.
A friend of mine put a little RBTA in his 110-gal reef tank about six years ago. It has cloned itself quite a few times since then. It overtook everything in his tank about four years after it was introduced. In the past six years, it has produced about a hundred clones. He removes them on a regular basis but it's hard to keep up when you have three dozen or more in the tank all cloning themselves.
This is what his 110-gal tank looks like today:
