The tank looks a little young, but in spite of your water changes and using AB+ this is likely a trace element issue. I suggest the following:
The Jason Fox solution to everything – Water Changes! 4 to 5 20% water changes over a few days, then continue moderate weekly water changes.
No Reef-Roids as standard food (very high phosphate content).
Start by dosing Tropic Marin A- & K+ per label.
Dose Brightwell Aquatics Ferrion. Don’t follow the directions on bottle, only dose 1ug/l (0.001mg/l) once or twice a week. This will probably be only a few drops each time.
Perform the very sensitive Oceamo ICP-MS test (see Reef Moonshiners Webstore), and correct trace elements. Especially the ones that deplete quickly:
Cobalt (B12)
Iron
Manganese
Selenium
Chromium
Copper
Zinc
Nickel
Continue to monitor trace elements with ICP-MS. Note - Standard ICP will only identify elevated levels, but not depleted levels of many trace elements. ICP-MS is a must!
If a trace element deficiency is corrected, you can expect a pretty quick and significant improvement in as fast as a few days, and also a shift in the tanks biology. It may go through some ugliness as the tank re-balances, and unfortunately you may also have to deal with some pests. But give it some time, address the issues, and that should do the trick.
It’s not your current problem, but for SPS I would consider slowly lowering Nitrate to around 5ppm, and phosphate to around 0.050ppm.
Plenty of folks run successful tanks without dosing trace. I don't think trace's are causing browning and bleaching issues for OP. (note, I run moonshiners and like it)
OP, what are you using to check par? What test kit are you using for alk and how old is it? What are you using to test SG? I too had a lot of issues like this when kicking off...my SG was way off. Hanna and Refracto (calibrated) would show up at 35ppt/1.026. When I finally bought a tropic marin hydrometer it showed 1.0285!....Needless to say that was a large issue I had to fix. How old is the tank? It looks young. Did you start with dry/base rock or live rock?