I tried hornwort from the lfs a couple times, never could keep it alive. Some years ago I received a shipment of dwarf crayfish bagged with some small bits of hornwort to cling to in transit. The crayfish died off w/out successfully breeding, but the hornwort is still growing like a weed. It very solidly fills the upper half of my 33 long, and has been grown under a regular FL shop light with 1 6700k and 1 10,000k bulb the whole time.
I also have Najas indica in several tanks. It actually grows faster though not as thick/dense as the hornwort.