Sick Plants, Late in flowering-Nute lock or def?

What is your experience level? (first timer, novice, experienced...)
First Timer
Your Equipment:
.1) Type and wattage of lights.600w HPS
.2) Distance from tops? 18 Inches
.3) Reflector type? DayStar.4) Is there a consistent fresh air supply? Yes
.5) Do you have an exhaust fan and a circulation fan?No exhaust, Circulation fan 4ft from plants

Your medium:
.7) Specific brand and type of soil, Fox Farm Ocean Forest, 2 part, Perlite, 1 part.8) Size of container.3 gallon grow bags
.9) Clones rooted in rockwall

Your nutrients and water:
10) Source of water? Tap, 6.6 ph
11) Method of checking water ph. ph pen
12) Method of adjusting water ph. Have not adjusted ph of water
13) Specific brand and N-P-K ratio for each bottle. I was using Humboldt Nutrients Bloom 0-6-5, adding 3 ml/L of water, now switching to Age Old 5-10-5 and Age Old Liquid Kelp Meal, 1 tsp of each/gallon of water, to be used every other watering.

16) Are your ph levels stable, or do they fluctuate? Stable ph levels

Your growroom:
19) Indoors or outdoors? Indoor
20) What size of closet, room or hut? Room
21) What are the temps and humidity levels while lights are on? ...With lights off? Lights on temp around 88-91, unknown humidity. Temp with lights off between 78-82 Degrees
22) Have you seen signs of insects in the growroom? NO!!!!

Your strain:
23) What strain are you growing? Durban Poison(Sativa dom) Blue Hen(Indica dom)
24) From seeds or clones? Clone
25) Is this an autoflower strain?
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My leaves are a lush green, seem healthy on blue hen girls, but the durban poison girls are lanky and leaves are yellowing, turning to brown and drooping. Is there any saving them? I am 6 weeks into flowering, and buds look healthy, just the quantity seen from past experiences. What is my problem? Is there any way to boost yeild at this point, or will i just be lucky to save them? Thanks in advance for any advice.