failure to thrive

[sea gnome]

My tank has been doing really well until about a month ago. (3yrs, soft and hard corals). My 2 cleaner shrimp died within two days of each other.( 3yrs old) and then the frogspawn that was big is still alive but barely, and today I noticed that the mushrooms are disintergrating. What is up?. Temp 80 fairly consistent, lights are 4 months old, no chemistry problems other than pH is 7.7 which I have trouble keeping at 8.0, it is the only culprit that I can find. Fish seem fine. Rachel