On the whole your girls are looking great There's a just couple of things that perhaps you may want to consider if appropriate.

Your using RO water, are you adding in extra calcium and magnesium to compensate? If not then maybe CalMag or molasses is worth trying.
Are they getting a good wet - dry cycle between waterings? It could just be me but those fallen leaves may be showing a touch of over watering.
If your using test strips for reading PH then you may not be getting an accurate colour to read from the runoff water. The runoff water can be tinted by the soil. A PH pen is a wonderful investment and does'nt have to be expensive.
Using baking soda and lemon juice for adjusting ph for long term tends to have mixed reviews from growers.
Those very top leaves on a couple of those tops in that last picture look quite thin and slightly curled under and in my (allbeit short) experience that, and the lower leaves, tells of off ph and/or over watering.
Just food for thought. All the best with them, I'm sure they'll be great