lower leaves turning purple-brown

[Rusty Trichome]

hello all!

Hello

light soil, no addings
.8) Size of container. about 1.5 gallons

Likely getting pretty rootbound.

13) Specific brand and N-P-K ratio for each bottle. List dosages (quantity per gallon) and current feeding schedule. i use bio-bizz organic plant food, like 6 differnet bottles, following the instructions - note that the bottles are 3 years old, but smells fine. at the begining i watered every 3 days and in the last couple of weeks i water every two days

Your 3 year old nutrients are likely no good any more. Plus, 6 different bottles? What the hell are you doing to those poor girls...? Most of what cannabis needs can be found in a (fresh) 2-part or 3-part nutrient system. Additives should not be used until there is a need for them, and until you have the ability to understand why you are giving the additive(s) in the first place. Is you potting mix 3 years old as well...?

14) How often are you watering between feedings, and how much per watering? isn't watering and feeding the same? i give the plants water with food inside every second day now, about 0.4 liter for each plant

Not unless you're in a pre-fertilized soil. (Miracle Grow or similar)
For most major nutrient systems, they have a weekly feeding schedule available on their web site. You are currently giving too much nutrients in a pot that's too small for the root structure. If you are following bottle directions, be aware that some companies label bottles as a stand-alone product. (they assume you only use that bottle on your plants) This can easily lead to overfertilizing. When in doubt, go with the online instructions.
Feeding in soil is best done (IMHO) once or twice a week (following a weekly schedule) with plain, properly ph'd water inbetween if necessary.

16) Are your ph levels stable, or do they fluctuate? i cant tell as i can only check pH before i add the food
17) What is your ingoing water's ph? ...your runoff ph? idk

Test strips offer the same, cheap method of checking ingoing ph for clear water. (any tinting will skew the color-coded result...even with test strips) A ph pen would let you test runoff.

Looks to me like (if your ingoing ph numbers are correct) that either the nutrients are dropping the ingoing ph too low, or the soil ph is a tad low to begin with. (the 'claw' showing on a few of your leaves) and you are seriously overfertilizing her. I'd flush well, transplant to a larger pot, and at the very least cut-back to your base nutrients for flower. Every other additive you are using is overkill, and you are doing more damage by not knowing how to use 'em.
You should also think seriously about purchasing some fresh product, and do not fall for the marketing hype. Grow with the basics till you know how to troubleshoot the damage you're likely to encounter as a result of overdoing it.

Are you using any side-lighting? Just curious...