2nd week flowering yellow leaves rapidly increase

[Hbk]

Hello everyone, This is my first grow..outdoors indica variant. They are in day 15 of flowering (fliiped). In last 3 days my leaves are turning yellow at an increasing speed and making its way to top. Medium is soil with perlite mix and compost all of which are organic. I am from kathmandu(Nepal) the land of the himalayas. Though, environment is one of the idealist to grow and i keep watering them every 3-4 days. What is wrong with these.Please provide guidance

 

[ezenzyme]

You need small amounts of N during flower with your P and K, i dont know what you have avail to you but some liquid nutes or some guanos will be rapid relese.