Normally when Cannabis goes into flower, it devotes all of it’s energy in creating buds. Therefore it’s canibalising it’s own leaves to care for their ofspring. This happens even to the healthiest of plants, you can google it. So my guess is there is a lack of Nitrogen in your feeding.
Because actually based on the amounts of fertelizer you put In (I asume it weighs roughly 1kg/1Liter) you are feeding roughly the following npk (i don‘t have the weight of the fertelizer):
78mg/L Nitrogen, 78mg/L Phosphorous and, 175mg/L.
You can exchange the mg/L with ppm.
There are many studies done with hundreds of cannabis plants suggesting that a minimum amount of at least 160mg/L (or ppm) of Nitrogen is very much advisable. It’s a myth that they don’t need Nitrogen during flower since the plant grows nearly double in sice during the first weeks only. So companies are putting less in „Bloom“ or flower products, wich goes contrary to credible studies of Nutrition for cannabis.
Anyways, If you have any other fertelizer laying around that has an npk of at least 5-0-0 or 5-1-1, something along those lines, 1-2 ml/L would do the trick imo