What makes coralline algae bleach out?

Consistent water perimeters and not changing all you bulbs at one time should keep it from bleaching or at least minimize it.

When are you seeing the bleaching?
 
Keep your heat under 85 and if you see it start (it can happen very fast) turn off your lights. It's mostly a heat/energy input situation.
 
If this is a new tank that you've set up with coraliney liverock it's pretty common to lose a fair amount of it. Differences in stability, parameters, and light will make it unhappy. In a while if you keep things on track it will come back. Besides the particular disrupted colonies, there's also a few diff species on the rocks. So when it is settled in they have found their happy spots and when things get moved they all have to populate according to their new various placements.
 
On the glass at least, it happens to mine when I'm trying to keep nutrients really low with high capacity GFO, wet skimming, GAC etc. And I've always believed high lighting is a contributor as well.
 
I shuffled all my rock around in my tank a couple months ago. Ended up with a high phosphate and nitrate level. Mine looks fine on my rock but most of it on the glass and power heads bleached. It happens
 
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