My tank has been up and running for almost a year now and I've never really had any problems with coral health. Recently, I've been having issues. I had a birds next die about 3 weeks ago. It was showing good growth but we had a cold spell (-10 for several days) and I struggled to keep my tank up to temp and it fluctuated. It dipped to 75 and then I got it back up to 79. I think that was its demise. I've had steady temps in my tank since then but now i'm having issues with a few corals. Perimeters: Ammonia - 0 Nitrite - 0 Nitrate - 0 Phosphate - 0 Calcium - 445 Alkalinity - 6.104 Magnesium - 1480 PH - 8.2 Salinity - 1.025 Last Water Change - 4 weeks ago Pic #1 - Organ Pipe Coral - Has been closed up for a few days now. It did the same when it was really cold but opened back up nicely after that for two weeks. Now it's been closed back up. Pic #2 - Torch Coral - Has been closed up for 2 days now. It did the same when it was really cold but opened back up nicely after that for two weeks. Now it's been closed back up. When fully open, I've noticed it's kinda brown except the tips. Pic #3 - Bright Red Montipora Capricornis - This piece was doing really well and showing good signs of growth. The far right 1/8" is new. I noticed that it was starting to brown out and I thought it might be the lights so I moved it down to the bottom. It's continued to brown out. Pic #4 - Candy Cane - I've had this coral for about 7 months now and it was doing great. One day I noticed it was shrinking in size so I moved it down thinking it was the light (it was mid tank right under a light). Since then, it's continued to get smaller and now i'm starting to see the skeleton. Pic #5 - Can't Remember the name - This coral is about 5 months old and has been doing great. Yesterday, I noticed the white spots on the tips of a few branches. Is this growth or is it starting to head south? I forgot to add alk a few days ago and noticed it dipped to 5.554. I bright it up to 6.5 and then 7.5. Could this be the issue? All of my zoas, ricordeas, sympodium, pavona & acans are doing great! Anyone have any ideas as to what is going on with these 5 corals? Thanks!