Howdy. Thought I'd chime in for a sec.
Years ago I was in need of more space so I enlisted a friend/took over his basement and set up for max fun. To make a long story shorter...we did a few grows and experienced what you seem to be experiencing mid-flower. Everything would look good...then instantly take a huge shit.
I'm not a fan of adding in dolomite/ferts/etc in my mix. Once yer on that train you cannot get off. It's where the term "shit happens" comes from in my dictionary. Outdoors is the only place I supercharge dirt/add anything into the mix. Plants outside can process things faster/etc, IMO than indoors.
But I digress...
Hopefully the changes you've made will see this grow finish/work out for ya. If it does...change nothing.
![Very Happy :D :D](/styles/smilies/icon_biggrin.gif)
If it doesn't...on the next grow I'd go with the OF/a bit more perlite with no additions. From there, I'd be sure every watering was spot on on pH...like 6.2-6.5. The nutes will offer the plant all they can in that zone. And yeah...don't give em those recommended hero doses of ferts. It's a slow and steady game. If yer gonna push it...wait til flower. Even then...less is always more. And if it was me....I'd try tap water and bag the RO for a grow. It takes all the minors out of the water. (possibly causing problems?) Just a thought.
Anywayz....we struggled for a few grows at my buddy's place until we figured out we were seeing severe lockout after about 8 weeks or so due to the high pH. Got a pen. Bought pH down. Religiously tracked it every watering and checked runoff as well. After that, things leveled out.
I hope you can nail the problem. Just gonna have to ride the ride and see. Like was said above...you can't make multiple changes or you'll never figure out what is wrong. Best of luck!