Help, last few months have lost several corals

[hey1baby]

I have had my tank set up for about 2yrs - This is a 180gl. I have had smaller before (trying to say not new to the hobbie). I have never experienced anything like this before. I sort of neglected the tank the past few months (went back to school after many yrs) and I noticed that both of my brains (one moon one favite) had started receeding. Needless to say I lost both. Then I lost my 10" bubble. I then noticed my green lobo starting to turn white. I did a 50gl water change, and did a watch and see. To my dismay, he died and then my red and multi colored lobo's. My softies are all ok, OH....but one thing I did notice, is that I started to loose snails before I noticed anything else dying, about 5-6 (along with my pistol shrimp). I still have quite a few snails alive now. Now I am noticing the base of my Mickey Mouse Pavona starting to turn white. Now I have been keeping up on the water changes, and all water test come back fine. I run 2x 96wt actinic PC, 2x 96wt 10K PC, 2x 250wt 15K XM MH 1x 175wt XM MH. I skim, temp is at 79 - 80 and like I said water par's are fine. Any Ideas? I hope its not to late. I still have my monti cap (small) softies (leathers shrooms zoa's...to many to list) & anenome (rock).
Ph 8.1
Amm 0
Trites 0
Trates <5
Dk 8
Mg 1250
Cal 450
Phos 0

 

[theatrus]

When is the last time you replaced bulbs?

 

[hey1baby]

I forgot to mention, MH are 5mo. Pc about 1wk. Acclimation was done both times, and the bulbs replaced were a year old.

 

[hey1baby]

most recent pic (10 min. ago)

 

[Travis L. Stevens]

What's your specific gravity and how is it checked? Double check your thermometers to make sure that it isn't off any. When is the last time chemicals were used around your tank? Do you run carbon?

 

[hey1baby]

No chemicals near tank, have 3 refractometers salinity is 34ppt and 2 thermos. Have not run carbon since tank was started.

 

[j_gilbert]

make sure all your parameters are correct and then do a large water change. I would follow up with another water change in about a week

 

[hey1baby]

I just put some carbon in, cant hurt, only help. As for water changes, I did the 50gl and have been doing 10 per week. This weekend, I'll have to do another 50 to see if I can slow/stop this. I havnt seen any type of bug/nudi and its only the stonies that are affected. this is drivin me nuts!

PS....When changing the lights, I went from all 175 MH 10K to 2-250MH & 1-175MH 15K. I acclimated them for almost 4wks, but, far fetched, would this have anything to do with it? (yes, ballast were changed also)