So based on what you just posted.. there is a big variation between alk test kits. Personally I use Salifert for alk, and I know a few big coral retailers that do as well. When I test alk when I'm at line 54 it's completely pink. That's where my tank stays. 54 or 55. What you are describing sounds like an alk irritation to me. Your nutrients are high enough that 8 shouldn't be an issue at all, however, to me it sounds like alk irritation. Personally I feel there would be no harm in letting the alk fall for a bit. That said I'm sure you've done it the same way for years. For me, some sps just never liked alk at 8. Some have no issues at 8 or even higher. But past problems of tip irritation is why mine is 7.0 - Salifert.
The only other think I can think is you've changed salts and added gfo. Like I mentioned I have had bad luck with gfo. I don't use it at all. That said my highest tank is .08 (triton test). Maybe the corals have adapted to the higher phosphate levels in your tank and are reacting to you lowering it, despite feeling the need to. Stray voltage doesn't explain why it heals during the week. The only other thing you've changed is salt. My personal opinion.. alk.