should be fine for a long time, and yes ornates do grow quickly if fed correctly.
I've got a 10 1/2 inch del in with my big ornates and they dont bother it.
there were some people posts in the forum where their ornate swallowed other bichir which is close to its size, you could do little search on this, but I keep mine with sens that are twice smaller than my ornates and no probs so far.