Maybe consider just stopping the NOPOX first. That should have an impact. Maybe wait a little while before removing the protein skimmer. Slow changes are always better. SPS take a long time to grow and be happy, they get really unhappy fast and then it takes twice or three times as long to turn them around. Although people run skimmer less tanks successfully, skimmers certainly remove DOC's (to some extent) and help oxygenate the water as well as more stuff. If you remove the skimmer, and if you are not using carbon (I am not referring to carbon dosing) then you will likely need to add something like ROX carbon to help with the DOC's. If you add too much ROX carbon, that is bad as well. So.., since NOPOX is a profound additive, eliminating it's use will have an effect.
Perhaps consider getting your parameters where you think they should be, hold steady for a while and then add some SPS. Acros are so darn expensive that you don't want to be doing a lot of experimenting with them. Get your tank zoned in, do the boring testing routine daily when you stop your NOPOX, so you clearly see where your nutrients are heading and if/when they have stabled out. Then move forward with either more changes like taking your skimmer offline or if stable then adding more sps. Fish (bioload) and appropriate feeding are a great way to add nutrients to a tank as well. Just some stuff to think about. All of this is a balancing act and it can be really challenging to get it tuned in.
None of us are reef experts, we are all novices, some with more experience or maybe just more luck than others.