@joporeefpro I'm in an EXTREMELY similar situation as you, it's almost comical. I've finally gotten my sps to turn the corner in the last month and here's my 2 cents.
Large tanks started with dry rock (marco rock type) seem to take a while to flourish and go through phases to get to stable. Mine's almost a year old and I can tell it's not quite "mature" but getting pretty close.
Corals respond weird at times so I wouldn't try to determine issue based on coral color/behavior too much. Remember, in a tank this size, it's going to take a LOOOONNNGGG time for nutrients to build up and fill the rocks/sand. Everything is in the absorbing nutrients stage imo for both our tanks. So small tanks cycle/mature faster.
I would focus heavily on fixing the nutrient issue, 0 nutrients kills corals (trust me, i've done it on dry rock tanks multiple times). Now if you have TONS of nutrients going in and being sucked out immediately that's different but i'm guessing your just feeding the fish once or twice a day and you have maybe 50 fish at most? That alone doesn't do jack squat to raise nutrients in a tank this size that's so young.
I would remove the biopellets for sure and any other phosphate/nitrate reducers you have and try to get phosphate to at least .01+ and nitrate to 4+ as a bare minimum.
I started dosing stump remover off an on in my tank to maintain phosphates and it's made a BIG difference and saved some dying corals.
Also, your alkalinity (dkh) seems high to me for an ULNS tank. If i get over 9 things start to go south when there's so close to zero nutrients. I think you'll find most ULNS systems are in the 7.5-8.5 range.
I didn't see you mention an apex but I would recommend one if you don't have it (or some other brand). I have 2 - 800 W titanium heaters and a 300w heater that maintains my tank within .5 degrees no problem.
My tank stats so you can see the similarities...
118" x 56" x 33" plus 6" x 6" coast to coast overflow on the back
100 gallon sump
3 - 40 gallon frag/back of house tanks plumbed in (no refugium currently, though plan to add some day)
2 - hammerhead pumps (one 100% tank to sump, one 75% back of house tanks/skimmer and 25% tank and back)
10 penductors to boost flow in tank (i'm trying to go no power heads to reduce maintenance)
~1,000 pounds dry rock (marco rocks style, but another vendor), Seeded tank with about 20 lb's live rock from my old tank that i knew had no pests
6 ocean revive led's and 2 - 4' t5 bulbs (i'm only lighting front half of my tank until i get more corals, then i'll add another 4 led's and ~6 t5's)
Tank started september 2016
currently ~55 fish
400 ppm calc
8.5 dkh alk
1350 mag
.0031 phosphate (elos color test read zero, and ULR phosphorus hanna registered a 1 ppb which converted to .0031 ppm PO4)
.5 nitrate (red sea professional low range, though i've been dosing kno4 for the past week so hopefully up to 4 or 5 by now, and it's definitely helping as it has in the past)
par for corals mostly in the 250-350 range (apogee par meter)
also just used chemi clean on entire tank to kill cyano that was covering EVERYTHING and keeping my tank from maturing (about a month ago now)
if you don't have any yet, try some digitata, i've got red, green, and purple that grow like weeds and were a good start into sps for my tank. This stuff always did decent even when my acro's/milli's were dying or trying to die lol.
feel free to post here or send me a pm if you want to discuss more. We are in a very similar situation for sure lol!