First off, Even if you're doing everything right, it may never "recover". What you're looking for is cessation of any new chlorosis and/or new necrosis. Detailed observation of individual leaves is needed to know if your actions have had any positive effect. That being said, I suspect insect and/or pathogen whenever a single plant is effected. Furthermore, my actions in your shoes would always be to remove the affected plant right away. Call the cost of that loss "insurance" against the rest of the crop becoming afflicted. This is greenhouse gardening 101.
When the entire crop is equally affected, THEN suspect soil PH, nute probs, ect...Bottom line is quality commercial bagged soil almost never developes PH problems. If your feeding solution is PH'd you should be fine. Most folks tend to think PH and overcomplicate things. Over/under watering is far more often the cause of ugly plants.
