I was about to give up when I thought I had downward spiralled my entire system.
Well heck no, don't go and do that.
I've been keeping reef tanks for a long time - let's see, going on 14 years now. I don't have all the answers and never will. Anybody that tells you they do is the last
person I'd listen to. Anyway, most of the answers that I do
have come from learning from my past mistakes. We *all* go through times that our systems frustrate us so much, we're ready to pack it in. I've got this horrid nuisance patch of caulerpa growing smack in the middle of one of my favorite corals, and it's bleaching it to death. Can't figure out how to get rid of it for the life of me. Point is, stick with it, and succeed or fail (we all fail at times), you'll come out of it with knowledge, and you'll do better next round.
Regarding the salinity: Should I rely on evaporation to raise it? By this I mean to replace evaporated water with salt mix at the same salinity of the tank on replacement day. It may take a month to change it all the way.
That is exactly what I would suggest. If you feel it is going too
slowly, When you do water changes, use water with a slightly higher salinity level for the replacement water.