SPS Tank O Death

[michika]

I need some help, this is my last ditch effort at not shutting down my 28g long nano once I get my 180g up and running.

This is my tank journal for the 28g nano.

The problem is that my tank kills SPS, and only SPS. I can keep all types of livestock with no problem, clams, fish, inverts, zoas, LPS. When I put SPS into the tank its usually fine for about a week, good polyp extension, good color, then after that I start to see no polyp extension, then bleaching, and finally RTN (which usually happens over night).

I have a theory that the cause is the glass. I used appropriate silicone, my water parameters have always been in line, and I'm not seeing anything picking at the SPS. Everything else in the tank seems normal; I have coraline growth, macro growth, etc. I use RO/DI, and have no problem algae. In short everything seems normal, but something is out enough to kill SPS and only SPS within 2-3 weeks of being placed in the tank.

Some quick details about the tank;
-Been running since Nov 07, upon my move from my previous cube ALL my SPS died, along with the bulk of my clam collection. All inverts, fish, lps, and zoas all survived.
- Parameters are as of April 15; SG 1.025, Ca 440, dKH 10, Mg 1300, Nitrate, Nitrite, Ammonia, and Phosphates are 0.
- No cleaners around the tank.
- Regular weekly maintenance schedule
- Running 175w MH in Luminarc reflector
- Tank is 12"x33"x18", and water height is actually 11"

I've posted this on RC and got a pile of suggestions, I explored most of them, but nothing came of any of them.