The best thing to do it to get it to attach to a small piece of rock or rubble. This allows you to slowly move him up toward the light so it can photoacclimate. They can handle a big drop in light intensity much easier than an increase. If he is getting more light in your tank than where he was before he could be squirting himself off to try to get away from the light. By having him attached to a little rock you can move the rock and attach it, so you wouldn't have to wait until it attached.