My hornwort grew about an inch a week in the oscar tank, but he'd brutalize it and it clogged up the filters. Overall, it was growing faster than he could tear it up, but became too much of a chore to keep fastened down. Nitrate is always high with 2 11-inch fish, so I suspect that is a reason the hornwort grew like crazy.
I'm experimenting with java fern in there now. It was growing a beard type algae in the betta tank, so I transplanted in where the pleco lives. Will he eat that nasty algae? ....we'll see I guess. Love the java fern, just weight it down and forget about it.