Now you guys have got me thinking allsorts of possibilities. I was coming down to either of 2 possibilities....
the mussels which were purchased frozen then put straight into my freezer. Before feeding I thawed in a little tank water the same way I feed all frozen foods.
The other strong contender for me is the oxygenation in the tank....during the water change yesterday I filled the tank a couple of inches higher than normal thereby reducing the water agitation from my spraybar. Also since getting the Tang and the foxface they have been going to town on the hair algae that was in the tank this will obviously raise the CO2 in the tank(this would also account for the reduced ph value of 7.8) as less photosythesis from less plant-life end product less O2. Since I don't run a fuge this i would imagine would have a big impact on oxygenation in the tank...?
Well spotted aquaman77 the chemicals I use at work include a very nasty substance called Permethrin this stuff is lethal to all aquatic life. So you can be sure I wear gloves at all times, and wash hands a couple of times at work, shower when I get home the hands are scrubbed again prior to working in any of my tanks. The day I did the water change on the FOWLR tank I also did a w/c on my Malawi tank with no ill effects there.
Wolverine all of the soaps/creams we use at work are non alcohol containing. In the house I use std soap but i rinse very scrupulously(its my wife's running joke that i am like a surgeon 'scrubbing up' before i clean a tank...)