What you are seeing is the clasic beginning of a nutrient deficiency. It would do you a lot of good to repot into a larger container. First your roots have to grow in order for your plant to get bigger.
The more roots you have, the larger your yield will be. Try not to flower in containers smaller than 5 gallons for this reason.
The yellowing of the leaves is a common nitrogen deficiency, the other stuff can be easily remedied with a good micro-nutrient like cal mag.
Natures nectar is a great nitrogen sup. to use in addition to the plant food you are using already.

use 1-3mL of cal-mag per gallon
add 5-15mL per gallon of Natures Nectar nitrogen.

As small as your plants are, it would be best to repot your plants in larger containers. Doing this will help correct defficiencies by itself. to avoid plant stress, just use plain water for the first watering after repot.
Once the plant is over any transplant shock, feel free to feed.

FYI, buy an HID set up for flowering. floros do a terible job of producing bud and stimulate tons of leafy growth during flowering. floros are great for a day or two after transplant. using floros after transplanting reduces plant stress. if you buy an HID set-up, buy an HPS 400w set-up. cheap, effective, and easier to cool than larger lights. It will still produce much more bud than floros and quality will be far better.
Also, floros give off very little UV light. Cannabis produces resin in response to UV light. less UV, less resin production.

Hope this helps.
Grow on...
GanjaRobPDX Reviewed by GanjaRobPDX on . 4th week troubles, please help. Indoor (closet) FFOF soil 34,000 lumens using clfâ??s/ floro tube tap water phâ??d using simple ph up/ph down kit plants are 4 weeks old all water until I watered with FF grow big last night Home made tent gets fresh air in with a fan, and bathroom fan ducted into the wall gets air out, keeps around 86, has peeked at 90 briefly until I adjusted. 24hrs of light for the last 4 weeks, was planning on going another week or so before flower Ok from the information I have provided here is Rating: 5