If nitrogen levels are your only problem then you doing pretty good. My biggest problem is waiting I want to pick these gorgeous Buds and smoke them right now haha
I'm somewhere around 50-60% of the drain to waste numbers right now at week 3-4 of flowering. GH trio + liquid koolbloom.
I've been led to believe 50-80% is a nice point to settle at regarding liquid nutes, GH trio mainly.
Have you ran GH before with that same strain? I know with my SFV on my first run I had the same problem as you were having running my line at 80% with koolbloom, the problem continued on. My second run with it I was 100% with the drain to waste feed schedule + koolbloom and a little calimagic by week 2 of flower and haven't a seen any type of yellowing since. Week 4 I backed off with the calimagic and all turned out great. All strains have their own needs. Just takes tweaking