You are doing something that can be quite challenging sometimes. That is mixing prenuted soil/medium with organic nutrients. Sometimes they work well together and sometimes they struggle due to chemical incompatibility. I cant remember if the FFOF is ALL organic or if it has some synthetic nutes, BUT I am less inclined to think pH at this point. Get some Epsom salt and some microbe additive to build your microbe herd in the soil/medium.
Any time you are doing organic, you must take care of the microbe herd first as they are the key to feeding your plants.
On the pH, when you add the Epsom salt, it will buffer the soil pH some which will help. The microbes seem to be happiest when pH is around 6.5 to 6.8 and with the FF soil and RO it may be a little lower than 6.5 in the medium (especially if the microbes aren't well established)
The one plant in the last pic does look like it is getting deficient in magnesium. So the Epsom salt will help that and the rest from getting deficient.
