Leaves still goes yellow after flush with pure water 6.5pH, then only water with Biobizz Fishmix and last time all nutrients but 50% of recommended.

I would try and get ph aorund 6.2-6.3, I believe your medium is soilless in light mix and BioBizz does well around that range. but 6.5 should not upset it to much. The lower growth does look to be nitrogen but the upper growth is showing signs of burning with the tips browning and curling up. If your following their schedule keep it up but alter the EC to match your plant, I like to use this guide for feeding autos, If your EC is to high it can cause lockouts and weird stuff. https://www.autoflower.net/forums/threads/med-man-method-feeding-chart-ppm-ec.47856/ Autos tend to feed less then photoperiods unless they crazy big in size, but even then its the same as a small to average photo plant. Good Luck!

issues with lower, older leaves is signs of a deficiency in mobile nutrients: nitrogen, phosphorus, potassium, magnesium, and sulfur. calcium for example is a non mobile nutrient and cant be moved from one part of the plant to another so those deficiencies show up in new leaves because they have to be pulled directly into the growing leaf it looks like nitrogen+potassium deficiencies (nitrogen the yellowing, potassium the browning and burnt tips) which can happen if the soil is too acidic, or if there's salt buildups in the plants. i tend to think its an issue of overfeeding, youve got a lot of nutes going in from reading the diary. check ph of runoff water if you're not doing so already not just the water you are feeding, and it might need a flush or some base to up the ph.