Corals doing bad after 3years?

I have a bunch of soft corals. Most have been in my 30 gal. for at least 2 years. All have been thriving. About 6 weeks ago, we started to notice most of them not doing well and it's progressed to where my Xenia is gone and my ricodea is not far behind. Candy canes dying too. Only the button polyps are still doing good. Nothing has changed in the tank for years, no change in routine. The water checks out as:

Ammonia:0

Nitrate:0

Phosphates:.025

Calcium:340mg.

KH:161

Salt:1.025

Any ideas?