Corals Dying! Help!!!

I have a 90 gallon tank that's had corals in it for several years and they've all been doing great for a long time. Over thanksgiving I had my grandma come and feed the fish while I was out of town (she's done it several times before). I was gone for about 3 days, when I got home I had a few problems. My encrusting coral is starting to die high up in the tank but the part that is lower is doing fine. Also part of my anemone is looking shriveled but the other half is just as normal. Any ideas on how these could go from good to bad so quickly??? Also, I know in the past poor circulation leads to red algae growing on sand however I have lots of circulation and haven't had the problem for a long time and out of the blue the algae is growing again. The standard ph, alkalinity, ammonia, nitrate tests are all within their correct ranges. Any suggestions on the coral/anemone and sand????

Welcome to the forum... I would do a check of your chemical levels first, then we can recommend a possible solution. I would say if you have the ability, I would do a 20% water change just in case.  Have you made any other changes to your system besides going out of town?  

Test kits do go bad, so I would take in a water sample to a store or a friend. This will help to insure that you are getting the right readings for the parameters..