Anacharis has been hit or miss for me actually. The first time I ordered some, it melted within 24 hours. The second time, it grew to twice its length in 24 hours. So I'm guessing if your water conditions match where the plant came from, that helps. I also tend not to leave it floating. When it arrives I cut about 1 inch off the stem, then rip the leaves off the bottom 2-3 segments and plant the stem. The original plant will tend to die off in a few weeks but not before sending out at least one new split shoot that I can plant.