Bleaching question

[Kynzo]

Had the tank up for 2 years now, I had a problem with bleaching before from what I believed was underfeeding and low nitrates. I started spot feeding once a week and got more fish and seemingly fixed the problem. Then for the past 7 months things were good, I saw growth. Now in the last month and a half I've seen growth slow grestly and a few lps having tissue receed. It's been slow recession so I don't think it's any bugs.
Parameters are
78 temp
1.026 salinity
Alk was 8.3 a few months ago but I just tested and I see its gone down to 7.3.
450 cal
1260 mag
No3 - 25
Po4 - <0.1
I change the water every other week but since I saw the tissue issue I upped it back up to every 10 days. I thought the Alk would be the problem since it looks like the only thing out of line but it still isn't terrible. Anyone have any ideas? I thought I had things on auto pilot with water changes being able to replenish my major and trace elements since I don't have a lot of Lps and the ones I do are frags. My lights are also reading from 40-120 par where my corals are. Is it the Alk or could it be something else? Thanks

 

[MnFish1]

40 - 120 par seems low - has it always been there? 7.3 alk is not that bad. Any other changes over the last 7 months?

 

[Kynzo]

It's been like that for pretty much the whole time. I only have lps and soft coral. The majority of the tank is 80 but at edges it's 40 and at the top of the middle rock it gets up to 120. None that I can think of. Lights same, flow same, parameters are as listed and pretty steady.