Big problem: burn tips and spot on Leaves

This might be because it is too hot for your plants, or the light is too close for them.

Also a little heavy on the Plagron PK, the label states a max of 1 ml/litre and that stuff is powerful...

I believe your lamp to plant distance is the problem. Raise them to 55/60 cm and you should be golden.

Have you checked your soil pH? If that's in order I believe it could be simply heat stress, I see your temperatures are 28-30C and RH60%. I'd try to cool it down and add a dehumidifier, RH 40-45% would be ideal and temperatures 20-27 rather than constantly above 28. High temperatures makes the plant want to use the water fast, but with high humidity their transpiration rate slows down. I know it's a struggle in summer though but good luck!

If it's just the tip that's too much nutrient but if u haven't been overfeeding then next thing is your light.. They burn out the cal/mag/iron out the soil fast so after around 3wk you should start feeding some cal/mag most come with iron and extra need minerals.. Good luck