Green stipe mushrooms shriveling

Just yesterday I noticed that my green stripe mushrooms are starting to shrivel up, all 5 of them, located at 2 different areas in the tank. My ricordea, blue and red shrooms, zoas, acan and toadstool are doing fine. The pH i noticed did drop to 8.0. I did a water change and rebuffered. The green shrooms are the oldest corals I have in the tank (about 4 months now).

About how long before I start to seriously worry about them?