Just a comment. Corals do not lie, if they are unhappy 99% your water parameters are not right. This is regardless what your test tell you, your test can state everything is perfect right on point but try to explain that to a dead coral. The other 1% is something else like light, bumping into coral etc…I don't think I need a high range nitrate tester though, can't detect it at all on an api kit that I can detect anything over 2.5ppm on, and it's been doing wonderfully for 5+months until this bacterial bloom caused me to move it, maybe it's damage from the bloom maybe it's the new light and tank I'm not sure.
Also from my experience high Alk and zero Phos leads to disappointing results unless your are 0.1% top Reefer and you know instinctively how much amino, fatty acids etc… to provide to your corals.
Last corals need food and they are superbly adapted to hunt for food, they have lot of mouth to feed. Light is not enough to keep corals growing, consider light as the gas pedal but you also need proper coral food (fuel for corals). Or they stall and perish. Favias are generally tolerant and it can take months for them to show signs that things are not going well.
Hope your Favia recovers, good luck