Don't be sorry... I'm the one asking!Have you considered that some of your soft corals may be releasing toxins, etc- ?
Your Ph - though its not terrible - and I dont usually concentrate on pH - Does it or your alk fluctuate when you are doing 'so much water changing'? Honestly - it may be that you are doing 'too much'. 40 gallons of water changes - 2 times a week (or did I misunderstand and you meant every other week - biweekly can mean both)
Lastly - where are you sourcing yoru corals, etc - Some from friends like you said - is it possible you have some coral damaging pests (AEFW, ETC) that could be causing some of yoru problems?
Is your PAR meter accurate (and your other tests)? Is the color spectrum 'correct'?
Sorry to ask so many questions - just some things I thought of.
Yes... I've considered it. I've run carbon, doesn't seem to make any difference. With the volume of water changes I'm doing, I don't think it's softy toxins, but yeah, it's on my list.
Bi-weekly, in my case, means every other week. Basically, 25% every other week.
Coral sources, local. I'm taking frags from tanks that I look at all the time, and have been healthy for years. I don't buy online. Could I have a pest? Sure... but if so, I can't find it. I've done spotlight inspections, magnifier lens, etc. Once again, it's on my list... can't rule it out, but it's nothing obvious, and I've dealt with flatworms and such on several occasions.
Kessel spectrum AB+... it's fairly specific. Borrowed two different par meters now, both read the same.
Keep the suggestions coming... even though I haven't seen anything new yet, it's nice to know that many of you have the same suspicions that have been keeping me awake nights