Maybe you overdosed a little?
90 Gallon tank:
Assuming a 4 inch average DSB (which contains, let's say, 50% water by volume) and a water level 1 inch below the toprim of the tank there is about 76 gallons of water before you consider live rock.
I'd guess that 125lbs of LR must be taking up about a third of the remaining water volume, so that leaves us with about 50 gallons in the main tank.
Assuming you have a 2" sand bed in your fuge and the water is 1 inch from the toprim, we can add another 3.5 or so gallons for a total of 53.5 (ish).
Add 5 gallons (guess) for the water in your piping and skimmer and we're up to 58.5 gallons.
Add to this the volume of water in your sump and we're probably still short of an 80 gallon dose.
I made a few assumptions there,, an inch of water height here and there makes a big difference,,, and I included the water contained in your DSB which I probably shouldn't have, as it's not circulated like the rest of the water in the system,,,,,, but I'm still amazed at the disastrous results. It's not like you overdosed by a factor of 2 or 3.