Problem or not? - 1st indoor grow

So, 90+ days into the grow, and the girls have been on 12/12 for 27 days. All six have been showing yellowing on the fan leaves, starting low, and now progressing upward. Other smaller leaves are also starting to yellow. The buds look fine - getting fat and sticky with no signs of problems. I am assuming that the yellowing is part of the natural cycle without some other sign of distress. Have been on dyna grow bloom food for the 27 days, a 4 - 12 - 8 mix.

The pics are yellow due to hps lights, so it is a little hard to tell the color.

I have tried to microscope for the trichs, but can't get the little hand held to hold still. Will need to get something because I think harvest is right around the corner - what do you think?

Sounds like they are right on track, and looking pretty good. You might want to look on Ebay and buy a cheapie microscope, while you are waiting for them to finish. I got one for less than $20, and 100x works great.