#ed_op#DIV#ed_cl#yieks....sounds bad ...the white sedements might be ich sometimes caled marine white spot...If you have a copy of the "Natural reef aquarium" there is a section on common marine illness on pages 253 to 255 that cover what you might have going on. The apearence of white dots on the one fish and the tendancy to srcratch on the Live rock is a good sign of ich a common parisitic infection which can be treated with copper medication. but be warned inverts WILL die if you atempt to use the medication in the main tank so it is imparitive that you isolate the sick fish imedatly (sp) this will aid in halting the spread of thedesies and prevent any other fish from getting it. but sadly there is a very good chance that the infected fish may die. I recomend imedate isolatoin (sp) and treatment of those fish, yourLFS should have a medication avalible. I had a ich out break when i was youger in a fresh water aquarium it wasnot pretty I lost about half the fish before the medication took hold so act quickly. hope this helps keepus posted, and good luck.#ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl##ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl#tigersax7#ed_op#/DIV#ed_cl#