Autoflower problem

A question from a fellow grower:

I have three autoflowering white widow and I am in the 4th week of flowering . I face the following two problems :

First problem : In one plant three leaves are turned down from left and right
side and they started become yellow from the top corner and all around
the leaf . The center of each leaf is still green . These leafs are
above the center of the plant . This problem is seen only in one plant .
Attached photo No 1714 .

Second problem : In two plants I see some leaves which become yellow on the
corner from each leaf . All the other part of the leaf is still green .
These leafs are on the top of the plant .This problem is in two plants .
Attached photos No 1717 , 1721

The third plant seems fine until now .

I have the plants in 5lt pots and I used as soil from the beginning peat
with perlite . I give them water once a day approximately 400 ml to each
one . I always have the water ph around 6 - 6.5 but my soil has always
ph more than 7 . I gave the plants 3 times during week 3 and 4 each time
2 ml of an organic fertilizer called NIRVANA . My light is HPS 250 KW SYLVANIA and my grow box 60 x 60 x 1.60

I would ph 5.8 - 6.0 and see if that helps ?

The pH could certainly go down a bit, assuming your way of measuring the soil is accurate. But the other culprits could also be a build up of nutrients in the soil. A EC or TDS reading of the soil as well as the exact pH of the soil might help us help you.