I find that for some corals, the color is a dark green when they rtn and others are white. It seems that acropora mostly from bali for me always turn green when they die. Mind you I've only ever had two instances where this has happened.
They look like this
. (Sorry I can't "right click" to get the appropriate photo info on my mac.) For me its only been the Bali acros that are purple with blue tips that have this coloring underneath. In this particular picture the RTN happened over night, so I'm very sure that it isn't an algae growth.
pH went down a bit, lowest point was at 7.9 for the evening.
I've been watching and watching for red bugs, but can't see anything. I am going to be treating my corals shortly regardless. I only ever saw them on one coral before it RTNed and I haven't seen them since.
Tonight I'm going to start back with liquid reactor, and hopefully that should start to get things back on track.
The more I think about the situation the more I think its chemically related. None of my fish or invertebrates are suffering in any way I can see. All my soft corals are growing like weeds, and clam death aside (as I believe it was just a bad coincidence), things seem to be flourishing.
Everything seems to be fine until something begins to RTN, once it begins, that particular coral is gone before anything can be done. And since nobody knowns what triggers RTN, I, as I'm sure many others have, feel helpless.
Focusing on the RTN as a result of a water quality issue then seems to be the next logical step. My corals are getting enough light, they are actually recieving about 2 hours less per day of MH exposure then they were a couple of months ago. We regularly correct our dKH, probably about every other week. Calcium is above where it should be so we've stopped dosing for the time being. We started to begin to drip Kalk, but tapered that off until we can find out the cause of this issue. I feel spriulina, frozen mysis, krill, and formula-1 pellets. I do wash the frozen foods before feeding them as well.
What about if electricity was leaking into the tank? Perhaps at such a low level that it doesn't bother the fish?