Have you changed anything with your lighting? More power? Leave them
on longer? I've noticed that the anacharis doesn't get as thick under
high intense light as it does low light. The anacharis I at my LFS is
usually a few inches long and rather thick when I buy it, howerver when
after it is planted in my tank for a few weeks, it gets very long very
quickly, but never stays as thick (I have about 3 watts/gallon).