This post caught my eye and it's like de je vu.
My nems also bleached after I went on 2wks o'seas holidays and I lost my green mandarin ( shouldn't have had him either -LFS- but my target mandarin is still looking good ) and lost a few corals later on. High nitrates were my problem after the holiday and I sold a number of fish after listening to advice on this forum.
They are great on here! Thank you experts : ) I am learning and growing...
The LFS told me after 6 weeks of cycling my new sw that I could have nems and I bought 2...they did fine for 5 months as did my corals so I thought it was a breeze- what was the fuss? My water parameters were great..then the ich, nudibranches, sump issues, crabs, giant bristle worms etc.
I understand your frustration as sometimes it appears there are no clear answers- much of case by case/ trial and error and various advice from experienced members. My issue was water quality- I hope that's the reason? One of my nems has gone further downhill after I upgraded my lights to 4 x 24watt T5s ( 167 litre tank) to "help them". He is in recluse at the back of the tank behind rocks and stretches his trunk to reach out to light and has withered so I think it's the light which has stressed him out? They will definitely move if they don't like something.
To top it off, the LFS I went to today told me to put another 1 or 2 nems of the same species in the tank so they can share the zooxanthellae???? I walked away totally confused along with other advice they gave ( adding more nems adds to the bio load and nitrates which got me in this trouble ).
Anyway. Just saying it can be daunting and take on board all the advice you are given and read other posts to learn when you get the time.
I will watch this post to see how you go with your nems and any advice which I may be able to learn from..
Good luck as I need answers to mine too.