The Christmas Tree worms were purchased in June, 2004. They failed to thrive in my big tank, so I eventually moved them to the smaller tank, where they are doing very well and growing again. I have found that filter-feeding type animals thrive in the smaller tank much better than the large one. The water flow is more diffuse (it has a manifold), it tends to be a bit more overfed-- not sure, really, what all the factors are, I just know that the small tank is where these tricky things do well. A few months ago I bought a hard tube worm for the large tank. It had two heads when I bought it. A month later, one head was gone. I moved it to the small tank, and now the 2nd head is regrowing. I wish I had a better handle on WHY these differences occur so I could be sure that my next tank (planning a 180) will work as well as this little one does.