Tomato, Chilly, Lady finger and Bitter Gourd leaves having burn marks and curling | Plant diseases | Commercial Hydroponics farming

Hi everyone! I'm quite new to the world of hydroponics. I'm facing some issue with my tomato, lady finger, green chilly and bitter gourd plants. All these plants were growing nicely and even started flowering. Tomato and lady finger had started bearing fruits. From last couple of weeks the problem started with my plants.

The leaves of my tomato plant started having burn marks at the edges and curled up. Lady finger leaves started having brown patches at the inside. Green chilly leaves too started curling. And now even my bitter gourd leaves started having brown patches inside. Before the brown patch, the bitter gourd plant was looking unhealthy and wilted. Please refer the pictures attached.

I'm maintaining a pH of 6.3 for the nutrient solution and using the same fruit mix for tomato, lady finger and green chilly. And using veg mix for bitter gourd. Taken the recipe from this site.

Please help me diagnose the cause for this and what do I need to do to recover my plants? Thanks in advance!!

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