Discovery of the day ...
 

Today I discovered a population of flatworms on one of my live rocks..... Looked around the tank and they ( maybe 30 of them) seem to be concentrated on the one rock. What is my best line of defence?

Are they the red flatworms? Those are the bad ones. A search on flatworms, planaria or flatworm exit should bring up numerous threads on them. Natural predators are some wrasse,s like the six line wrasse , yellow {banana} wrasse, mandarins, even yellow tailed blue damsels. All these are a 50/50 shot at eating them of course and cant keep up with their reproduction rate if they get going. Siphoning them out helps also.

If going to use "exit", read up on it good and be aware of the toxin produced from dead flatworms.

Thanks Doug..
they look like these ones.
http://i649.photobucket.com/albums/u.../flatworm2.jpg

u could try a nudibranch that i think is called blue shields who specialize on eating flatworms, they are worth a try:mrgreen:

just buy flat worm exit. i had a small population similar to yours and it took care of it in 2 doses.