This is normal. They eventually wither and die. As long as your new growth looks good (it does) then you're fine. I do see some bleaching or something on your lower tips and to be honest I'm not sure what that is, hopefully a grower here may.
I do know that 7 is a little high for pH, if barely. Give it some swings between 6 and 7 or shoot for 6.5.
I'd also consider re-potting this lady VERY soon!