Read through the thread... I'm no expert and I struggle to keep acros myself... but in my opinion there are too many changes being thrown at this tank to help. If this was my tank I would start with 1 thing at a time and work my way into every solution over time.
1) Test and adjust par - I'd leave this for 2-3 weeks to see if there are any changes to the tanks condition
2) If no noticeable improvements I would reduce the Nopox dose from 1ml daily to 1ml every other day - try this for 1-2 weeks
3) If not noticeable improvements I would completely stop dosing Nopox and closely monitor nutrients for also 1-2 weeks
4) If things still are not improving and NO3 and PO4 are 'limited' I would look at adding more fish or feeding heavier
5) Reduce the skimmer run time
6) ICP test - you could also do this right now just to double check
7) If things haven't shown improvement by now I have no idea what to tell you - I'm just as lost as you lol
But really I think all the solutions provided are valid but you have to consider that everyone making a suggestion to you implemented that individual solution vs throwing 5 different changes at the tank. Also IMO if you do too many things all at once... you will never know what the 'smoking gun' was. You and everyone on this thread will never learn what solution helped. Just my 2 cents and I hope to see updates showing a turn around for you!