bleaching start from tips down followed by base up

[pkirby]

I recently lost a coral that appeared to be doing great for about 2 months until one day I came home and the tips of the coral had turned pure white (was previously a bright green) each day the tips had a little more white on them. After about 3 days the base of the coral started turning white. In about 3 more days the coral was lost. This is what remains:
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/PxO55vI5meetJNsteXn30_Z8ownjHz1iUPBEr6KIChI?feat=embedwebsite"><img src="https://lh3.googleusercontent.com/-W3hg8O0jDGY/TuKXoQfzbnI/AAAAAAAACVw/5e5Y4jclDsY/s144/photo%2525205.JPG" height="144" width="108" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/102786811550573904182/Picassa02?authuser=0&authkey=Gv1sRgCL_MoP_f28q94gE&feat=embedwebsite">picassa</a></td></tr></table>

About a week later, another coral is showing the same symptoms, and roughly the same timeline. Both of these corals were purchased on the same date. This is how it looks today:
<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/1NyBmwfNBn4Qq6_Enml0-fZ8ownjHz1iUPBEr6KIChI?feat=embedwebsite"><img src="https://lh5.googleusercontent.com/-EdGFbLhMsiE/TuKXkhxoR9I/AAAAAAAACVg/pN07ySZ2g5o/s144/photo%2525201.JPG" height="144" width="108" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/102786811550573904182/Picassa02?authuser=0&authkey=Gv1sRgCL_MoP_f28q94gE&feat=embedwebsite">picassa</a></td></tr></table>

Other corals still look healthy as ever, so I'm at a loss as to what may be causing this. I'm including some pictures of those corals at the end of this post...

My water temperature had gotten to 82 without me realizing. (I was using a digital thermometer, an old fashion floating thermometer pointed out that 79 on the digital was actually 82... anyway) I've dropped the temperature down to 79.

parameters were testing using liquid test kits.

Ammonia = 0
nitrite = 0
nitrate = 0
phosphate = 0
ph = 8.1
alk = 11
calcium = 480
temp = 79
salinity = 1.026

Aquarium is 75 gallons + 30 gallon sump containing skimmer and macro. Circulation is 2 - 1050gph koralia + 2 -750gph koralia. One 1050 runs full time. The other 1050 alternates every 15 minutes between the 1050 and the two 750's. Additional flow is from the Mag 7 return pump. It has been up and running since late April.

I assume someone else has seen this happen and hope someone can give me suggestions of what I can try to prevent this. Is there a coral dip I can use at the first sign to maybe prevent losing the whole coral? I'm scratching my head... I appreciate any help you all can provide!

As mentioned, below are some pictures of other corals in this tank on the same main rock as the one currently showing signs of bleaching. They look fine to me... They have all been in my tank roughly 2 months.

<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/YJ-qHp0zfuGk1qqgFc7II_Z8ownjHz1iUPBEr6KIChI?feat=embedwebsite"><img src="https://lh3.googleusercontent.com/-Ldi5Gujf4cY/TuKXllhOmKI/AAAAAAAACVk/xNwudN7I11I/s144/photo%2525202.JPG" height="144" width="108" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/102786811550573904182/Picassa02?authuser=0&authkey=Gv1sRgCL_MoP_f28q94gE&feat=embedwebsite">picassa</a></td></tr></table>

<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/HWKLGznmUz8W3Cp64SLW6vZ8ownjHz1iUPBEr6KIChI?feat=embedwebsite"><img src="https://lh3.googleusercontent.com/-MQBrqQ6EM5k/TuKXmkTG3pI/AAAAAAAACVo/xTfTwbNnOyg/s144/photo%2525203.JPG" height="144" width="108" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/102786811550573904182/Picassa02?authuser=0&authkey=Gv1sRgCL_MoP_f28q94gE&feat=embedwebsite">picassa</a></td></tr></table>

<table style="width:auto;"><tr><td><a href="https://picasaweb.google.com/lh/photo/mEkdaeXKnv6pUE3i2_dYhfZ8ownjHz1iUPBEr6KIChI?feat=embedwebsite"><img src="https://lh6.googleusercontent.com/-ZyEW9QD1zaQ/TuKXnpGJKsI/AAAAAAAACVs/DU5eOv7brgI/s144/photo%2525204.JPG" height="144" width="108" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="https://picasaweb.google.com/102786811550573904182/Picassa02?authuser=0&authkey=Gv1sRgCL_MoP_f28q94gE&feat=embedwebsite">picassa</a></td></tr></table>

 

[Acronic]

lighting? How did you drop the temp?

 

[pkirby]

Lighting is 4-54w t5ho and 2 ecoxotic panorama pro modules.
The temp being 82 was from my heater, I turned the heater down 3 degrees and my water temp followed suit, so although the heater is set at 76 now, I'm getting temp reading of 79 from my float thermometer. Temp holds steady, I have checked it several times throughout the day over a week and have seen no temp difference

 

[duke62]

Check carefully for aefw.cut off the white area and frag the living and dip it. If its not aefw check your alk even though alk swings you will notice if your caps are bleaching if you have caps. Also alk swing usually make coral stn from the bottom up

 

[pkirby]

What kind of dip? I haven't used any... I was looking up tlf revive, is it good or is there something else I should try?

 

[Acronic]

coral rx is another good one. 82 is fine, any higher and its time to worry. I would also be checking for pests. How do you maintain alk cal and mag?

 

[duke62]

i use coral r/x and also bayer insect killer i hear kill them and egss.def looks like something is eating your coral

 

[FIREFISHPAT]

alk is a little high, Some people would say that is ok for frags. I would bing it down a little,