Dying off - ideas?

The brown areas on this stony showed up about 3 weeks ago. I had my water checked all was good but ph was low. I since started using Kalkwasser and the tank as a whole is looking really nice except this digi is still yuck. Ph is at 8.3, temp 76, salinity 1.023. Any ideas? Iodine dip? I did move it from near the top to about 1/2 way down the tank. I also took a tooth brush 2 weeks ago and brushed off the muck but it's come back. Thx all.
 
Possibly dinos??? turn off your flow in your tank and after 25 minutes you'll see it floating in your tank or off your rocks... your salinity is low too.. raise it to 1.025-1.026
 
What exactly are your Ca/Alk/MG level's, if these are all in-line then your PH should not even be a problem. That looks like tissue recession with algae growing on the dead area's, I would also suggest slowly increasing the SG a bit but I don't think that is necessarily the cause of your issue.

Cheers,
 
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