i have a 4 year old 30 gallon reef tank that started to die off a month ago. the tank was truly perfect with not a single problem until i introduced a long nose hawk who didn't make the move very well. after a couple of days of being as boring as a hawkfish, he died and i removed him within a few hours his demise. about a week later my other fish started to drop out one by one. starting with the flame angel followed by a bi-colored blenny and a couple clownfish and finally the inverts; banded shrimp, cleaner shrimp and about a dozen hermits. these were all total veterans in this system and had survived long power outages and a couple of other stresses. in other words, pretty hardy little guys. what lived? a bunch of different mushrooms, most of the snails, a sand sifter star and boatload of zoanthids, though i thought they had died becuase they were closed and mucousy.(more about the zoo's to come...) throughout this process, i did several water changes(fresh from the ocean), changed carbon and vacuumed sand but stuff continued to die off. finally, once all of the fish were gone, i decided the zoanthids, which had basically overrun the tank might be the source of my problem so i removed all of the rock with them on it and scrubbed those little closed up nubbies off and gave the rock a nice fresh water rinse,(well water, not tap). other life on the rock did just fine(mushrooms, little feathers, etc.) i did take one piece with the zoanthids to a friend's system to see if they would open which they did. i feel a little guilty about killing all of those others for nothing but honestly, they were so aggressive, i'm sure they'll be back once i figure all of this out. okay, so THEN i did a 100% water change and started over with a few chromis. all of the fish died within 24 hours in my system. before it is assumed that these fish were stressed, i will note that the 100% water change came from the same system the chromis came from and fish were properly acclimated. at this point i assume that some piece of equipment is somehow polluting the tank so i replace the filter(whisper 60 replaced by penguin 350. yes i know a wet/dry would be better but trust me, this system was cranking), removed the powerhead and protein skimmer and proceed to cycle the tank with all new equipment. after a couple weeks and another water change things are starting to open up a little so i decide it's time form another chromis/canary. no luck. still a death tank for verts. the reamaining zointhids are about 1/3 open and the mushrooms look to be about 80%. something i didn't mention is that my levels throughout this whole ordeal have been GREAT. amonia, nitrates, nitrites, PH, Alk. all right in the zone. i use C-balance regularly and also add a little iodine. but there's clearly something nasty living in my system. is there a way to test for other disease? i'm very hesitant to throw out all of the rock becuase it's still thriving and beautiful. also, i don't think i can go on not knowing what the problem was. did that little hawkfish bring something with him that could be lingering? it's been recommended that i toss out all of my rock and sand and start from scratch but the mystery factor will keep me up at night. i HAVE to know! any way to test water more thoroughly than the off the shelf kits? something i might treat with that won't kill the rock?