First off your Ph is low! Get the res up to and hold at 6.0 (5.8 - 6.2 is ok). Higher not good but lower IS worse!
Stop the hydrogen peroxide use now! Put an air stone connected to an air pump into your res. Better yet use a 2 line pump and use bolth. Peroxide just evaporates from the mix in less then 24hrs...
The plants show stress from low Ph and CalMag dif. The low Ph is contributing to the Cal Mag,,but you are low on that too. You don't need to flush just yet.
USE G&H CALiMAGic at 5ml per gallon of formula in res. !!!! (the CALiMAGic is low N and contains some extra iron and you need that right now too)
FEED THEM....don't get flustered by what they look like right now. You have along way to go and this is an easy fix!!!
Be aware that the old leaves will NOT repair themselves. What I mean is this; See a problem - make an adjustment - see results in new growth!
In soil it takes 5-7 days to show a correction.
In Hydro it takes around 3 days to show a correction.
You will only see the "fix" in new growth from the top of the plant.
Soil has it's own problems for a beginner, like taking longer to just show a problem and then longer to show the correction....
In hydro, if you start out with a proven formula you will have a better chance at your goal (in soil too).
A simple rule of thumb would be like.
Pick a nutrient and follow the manufactures instructions...ALWAYS ad a CalMag product. (It's easy to stop if need be) and a good zyme helps root health in hydro more then most think.
You and the girls will be fine. Trust me. Fix Ph, add a Cal Mag product (stay away from epson salts for now) and in about 5 days you'll see recovery!
Good luck