Leaves starting to look yellow @ week 4

Starving for potassium............add a P/K booster to your nutrient line up.

Gottagrowsomtime is correct - if you're using Fox Farm nutes, you're locked out. The culprit is the grow nute... it has far and away too much nitrogen in it and after trying over and over again to get it "right" with that nute line, I just gave up and am SO happy I did. Since you're locked out, you'll probably need to flush your plant.... 3x the pot volume of pH'd water through her .... into the last gallon, add 1/2 strength nutes BUT cut the Grow Big down to maximum 1/4 tsp... and keep it there the rest of the grow. Once they've dried out, you can resume your normal dosage of Big Bloom and Tiger Bloom - but keep that nasty GrowBIg to no more than 1/4 tsp. You might also consider adding in a good PK booster at this point... something like General Hydroponics KoolBloom liquid would be good... the ladies are needing a lot of phosphorus and potassium as they build the buds... and you must ALWAYS pH anything you give to her... wild fluctuations in the pH is just asking for more trouble. Good luck..

Your PH is a little low. As the leafs up top look more yellow. I really don't think she's fine. She shouldn't be that colour She should be lush green. I think pers your locked out. Try Epsom salt, great source of mag/sulphate "slphur" 6.5-6.8 range for synthetic nutrients with soil. As these are hydro nutes.. I'm guessing they are bringing down your PH.. if your tap is higher. All is needed, is spliting your feeds with half fert and then after a few hours water with your higher PH tap, if it is higher. Good Growing.