Thanks for the reply. I've actually read all of that already, coincidentally published by you (you have amazing info by the way, excellent read - kept me up late last night haha)
I guess the part that bumps me is when fish die off before having much if no symptoms at all.
I've had 2 chromis die over the last month. The first I attributed to bullying. He was the smallest of the group, had some torn fins, looked a little beat up, but through my reading it seemed this to be a well known issue with chromis. After the other two shunned him, he stayed to himself for over a week before he eventually vanished. It wasn't till the second (who died yesterday) suddenly out of nowhere started to isolate, stopped eating, seemed lethargic, and eventually I found him rapid gilling on the bottom of the tank last night. Now, the third (largest, fattest, and healthiest) is super skittish and hiding a lot. He shows no visible signs and ate today, but I feel it's just de-ja-vue all over and wouldn't be surprised if he starts declining over the course of the week.
I have two clowns (not mated pair but bought together) who have been fine, happy, healthy for 2 months. An orchid dottyback I've had for 4 months, who I have seen flashing, but rarely ever has come out since I got him, a LM blenny (who I have also seen flashing) but is active, eats mysis and nori, and a clown goby who seems ok. Tank parameters are ALL solid and corals are all doing awesome, so not water.
The main red flag was a flame Angel I tried to introduce a couple weeks ago. He was a fresh shipment, but I watched him for an hour at the store before buying, acclimated him properly and went in the tank with no stress, other fish didn't even know. The next day he was out and about picking at rocks, 5-6 days later I noticed a couple barely visible specks on his tail, he'd swim up sideways to my fire shrimp (who wouldn't clean him) but still looked healthy. 2 days later, I found him dead wedged under a rock one morning.
This whole thing has me scratching my head.