I love hornwort...and it's not merely because it is one of the few aquatic plants that grows exceptionally well for me, although that certainly helps. I expect...and am rarely disappointed...that it will essentially die off when placed into a new tank or pond, with shedding needles and disintegrating stems to deal with for a short time. But then it always rallies and grows back strong and beautiful. I just had this occur in the spring when I placed it into every one of my outdoor stock tanks and my inground pond; the stuff pretty much fell apart, but new growth occurred immediately and it's done amazingly well all summer. In a few weeks when I bring a bunch of it back indoors, it will do the same thing: die off, make a mess, and then come back with a vengeance.
I've pruned it back several times already this summer, which entails forking out huge handfuls from each pond and composting it. I no longer use it in my DIY gel food, mainly because I have even more duckweed for that purpose and it blends much more nicely in the food processor.
But it feels great to carry a bushelful out to the compost heap a few times each summer. In contrast to my indoor tanks, the ponds get very little in the way of water changes. A bushel of Hornwort on the compost heap translates to a big helping of nitrates removed from the system.