Just what I thought . Ok . I keep looking at the type of pots you use and soil levels . I have a strong feeling you moisture levels are a problem , you are in a lot drier climate than me and every time you post and I can see the soil it looks dry , more so with the slits in the sides . Plus the use of perlte . You may be giving them plenty of water , but they are drying out to fast which leaves to much time with inadequate moisture in the soil , which leads to less nutrient uptake . So when you have added a nutrient to fix a problem it does not have the time to be absorbed fully by the plant next time you water . How do you water and how much run off . that also can make a big difference .