yea, maybe in hindsight, maybe should treat the aptasia first then go with nudi's after to get the small / remote / persistant buggah's
And yea, the mandy usually hangs in the back/corners... but on occasion i will see him in the middle.
gotta remember that all the other fish are trained to hang in the middle when you feed them.. the mandy doesnt give a rats You better mean it as in 'donkey' about you and your food, so to them, you are a predator, and reason to hide...
you might want to try weening him onto other foods, or at least give it a try..
talk to the resident experts on cross feeding.... (hello, GREG?.... Greg?... Bueller???)
And i wouldnt expect to see a change in perameters if just a mandy croaked... that is the difference between a mature tank and not so mature tank...
moving rocks and stuff around is way more harmful then letting your cuc get a big snack...
BUT, if all the shrimp and stuff died, then hmmm...
but at the least you should see the shrimp shells or at least one of them...
grab the flash light and wait until a couple hours after dark, and start lookin for them beady little eyes...