Need help figuring out sps balance (bleaching vs browning)

[Swell]

Tank parameters:
SG: 1.025
KH: 8.8
Ca: 430
Temp: 77.5
Nitrates: 2-5
24"x24"x24" cube

Radion G4 10" up: 100% at AB+ schedule (70% intensity) ~460 par in the hotspots, ~250 par mid level, about 100-120par on the sand. Acclimated from 50% over 12 weeks.
Photoperiod 10 hrs. Chaeto on 75w grow light in fuge 4 hours a night.
Feeding Hikari-S, Reef Chili, TDS Pellets twice a day with Eheim auto-feeder.
Flow: x3 Vortech MP10 (One on the left, 2 on the right) random reefcrest to 100%, then 8 hours night schedule on 50% tidal swell.

I've noticed over time, some of my sps will color fade towards bleaching, but the sps that are showing this, are actually lower in the tank than most of my other sps, even my yellow porites is showing symptoms. They won't fully bleach, but their color will just fade out.

For example, my stylophora, monti cap, pocillopora, and acropora are in a high light area (~460 par) and absolutely thriving, but the pieces exhibiting this fading are in about ~250 par areas.

The way it was explained to me some time ago was...
High light + high alk + low nutrients = bleach
Low light + high alk + high nutrients = brown

So my confusion is why the sps in the lower par regions show symptoms of high light, yet those getting blasted with light are just fine. What am I missing here? I've since dialed back my lighting to 90% (63% intensity), but have not touched the photoperiod.

 

[Big G]

Have you heard Dana Riddle's MACNA speech on Par, Photosynthesis, coral growth?

https://www.bulkreefsupply.com/vide...light-water-motion-by-dana-riddle-macna-2016/

 

[Swell]

I have now, thank you for that.

The takeaways to my situation are...
- The species of sps I am witnessing fade in are more than likely in photoinhibition vs the species in high PAR areas that can handle the chemical exchange better.
- I need to lower my light levels.
- Maybe raise alkalinity to ~10dkh

My flow and parameters seem on point, so it seems bringing the light down is all that is necessary. I haven't seen any alkalinity burn symptoms.

 

[Martin Kuhn]

The values you posted are very good. Didn’t you measure PO4 also? Maybe this is the make it or brake it

Kind rgds
Martin

 

[Swell]

I've never had an issue with po4 so I typically don't post it, but Hanna ULR says 0.01. I've never had anything above 0.04 according to my logs.

Also, I'm doing 5% water changes every 1 1/2 days, if that is a factor.
Dosing 30ml B-Ionic 2 part in 6 separate intervals through the day.
(32ml Alk/30ml Cal)