tank is crashing

[Delphinus]

Have you etablished a cause yet?

Because what immediately comes to my eye is that it's all (or at least mostly) SPS that is suffering. Which makes me wonder if it's not so much a "crash" but a very nasty bout of RTN. I am just getting into SPS and already I have suffered nasty losses of SPS just by introducing one little frag with RTN -- have now lost entire colonies because of it.

The other thing I noticed that you have a macroalgae refugium in your sump. This too can be a problem. I found that macros are an awesome way to pull nasties out of the water column, but if you miss a sporalation (sp?) man it take forever to recover from that if it's a significant piece that goes on you. Nothing like going from 0ppm NO3 to >80ppm NO3 in a matter of 24 hours. This has happened to me twice now. Ugh. For my NEXT refugium I want to go with more non-sporalating species of macros and keep the caulerpas and halimedas to a minimum (BTW, I can speak from experience, halimeda CAN sporalate on you ... not as often as caulerpa in my case but just as nasty an explosion).

Good luck!