massive fish dieoff

ok so over the last week something crazy has happened in my tank. I had a 40g tank and in it there was a baby hippo tang (a little bigger than a dime) a manderin dragonette, a cinimon clown, a very small goby, and a red spot anthias.

First the dragonette died (it was completely random as he was definately not starved), next the hippo bit the dust, the next day the anthias was gone, followed by the goby a few hours later, i got the cinimon clown out and put him in my main tank but it was too late as he was dead a few hours later. he looked like his skin was pealing and he was in respetory distress.

in the tank there was also a bunch of snails, a cleaner shrimp, a coral banded shrimp, a sand sifting sea star and a couple feather dusters. The feather dusters lost their feathers and turned black (they are still moving a little but i know they are about to go)... i had a star fish in the tank about 2 weeks ago. it got sick and i got it out of the tank as i know they are toxic when sick or dying. it was 2 weeks b4 the die off started so i am not sure if that coule be the case. all of my water perams are on target and my temp in steady at 79.4. i had the water tested at my lfs and its fine. was it the star that caused this fishy disaster

(ps i did a 20% water change the last 2 days in a row...

 

How long has this tank been set up and running for ? If new then how was it set up and cycled and the fact this anthias did is not to shocking or unexpected they are demanding type of fish .

 

Just to echo Tangster, the anthias are indeed demanding. My view is to never put them in anything less than a 72" tank. I wouldn't even put them in my 48" 90g. AND, they demand a more frequent feeding schedule.

The other fish? You did have something go on. Do you have any sea cucumbers in there? Anything that could have died and secreted toxins?

 

what are you useing to check salinity, I have heard of the same thing happaning with a hydrometer that was not floating right. personally I only use a refractormeter.

 

the tank is quite established (had it going for about a year) the tang was VERY VERY VERY small im talking less than a nickle in size. the anthias was about a 50cent piece. i tested the water at the lfs. he stated the water is prestene ( i cant spell) my temp is 79.4 my salt is 1.025 everyone was fine and dandy until the star fish bit the dust. but it died quite a while b4 the die off...