Help! Start of Slow Tissue Necrosis Event?

[ScubaSteve]

Alright, I'm a little worried here as I have something happening here that looks a bit like the start of an STN event. To help you guys help me here I'll give you a little back story...

I just recently moved my tank and in the process upgraded from a 20G to a 40G, keeping the same equipment but replaced the tank and the substrate. That was about 2.5 weeks ago. Within days of the move, everyone was perking up and even some of the pieces that were looking a little neglected were beginning to look great again. Awesome.

I have been feeding sparingly over the past two weeks to allow the substrate to catch back up as it was new (I only have two small fish at this point I should add, so I'm not feeding a ton to start with) and to avoid a major cycle... and so far there has been no noticeable cycle, maybe just a little blip when I first moved it.

I went away this past weekend (Saturday to Tuesday) and had my roommate look after the tank (by look after I mean feed a little bit here and there and top up the water). When I got home the sand bed was in disarray (courtesy of the pistol shrimp) and some of my frags had been rearranged (a la urchin). One of my monti's had been knocked off the rock by the urchin and unceremoniously dragged under a chunk of LR by the pistol shrimp. When I pulled the monti back out to freedon I saw that about half of it was white... like down to the bone. I was shocked (but weirder things have happened) and that monti had been stung that bad before and recovered just fine, so I didn't think a whole ton of it.

About two days later I looked at one of my acros and noticed it was white around the base, probably from being stung by the two mojanos that moved right next to it while I was gone. I moved it to a new spot away from the mojanos (which I have now removed) to let it recover.

Today I noticed that one of my big acro colonies is turning white around the base (mostly in the areas that aren't getting light) and my big green bird's nest is showing the same thing in a few areas (again in the low light areas). Now I an worried...

I few points:
-Everything has good polyp extension and other colonies are doing just fine (for now...)

- My aussie duncan has been reluctant to extend all the way for a couple days (it does do this sometimes) but there is no tissue recession.

- My new pulsing xenia (added a week ago) has stopped pulsing and is starting to look a bit "thin and whispy". My other xenia's are doing fine.

- My candy cane colonies are put their feeding tenticles out during daylight hours, which they have never done as I always feed them late at night. Just kinda weird.

- I haven't noticed any huge temperature swings despite the hot weather and a warm apartment (been working at home this week, so I've been watching it like a hawk). Keeps around 79.5F to 80.5F.

- I have flatworms. No the acro eating kind, just the ugly disgusting kind. They are not in plague proportions by any means.

Parameters
pH: 7.8 (kinda low)
Ammonia: 0 ppm
Nitrite: 0 ppm
Nitrate: 0 ppm
Phosphate: 0 ppm
Alk: dkH 7
Calcium: 480 ppm (high)

I use a brand new API Master test kit but I use a medical syringe to measure the 5ml of water (as the API test tubes suck).

Whew. Ok...

So my questions are...

Does this look like a case of a STN and it might be spreading through the water column? If so, how should I treat it?

or

Am I under feeding the tank (for reasons described above) and everything is starting to starve/weaken?

or

Are all of these things just happening at once (stings, new coral positions and areas of no light dying off, etc), aren't necessarily related and I should just suck it up and wait it out?

I've added a few pics so you can see what I'm talking about.

[Greenmaster]

I would watch the tank closely and if it seems to happen at night where a big patch disappears I would stake out the tank one night looking for a worm or some other hitchhiker.

[Seafan]

Hi, two things about your post that jump out at me, may or maynot be causing the issue;

1. is that you have doubled your tank size, but not your lighting, so you've cut their light by half.

2. Has your alk always been at 7? seems a tad low to me, and out of balance with your calcium.

sure hope it's not an stn event, and that it turns around for you.

[whatcaneyedo]

When my corals have done that its because they weren't receiving enough light and/or flow.