My intank refuge in my 10 gallon had alittle bit of rock rubble, but I never saw any bristle worm. Six months later while breaking down my 10 gallon, I found about 30 baby brisltle worms in the sandbed. I can only imagine how many where in the refuge. Just buy some live rock from someone that has an established tank or just buy rock from your LFS like I did. You will get the bristles and much more.