Hey man i dont ph the water I flush with, but my water runs 6.5-7 and the plants dont mind it so I use it just like that.
Anyway say the last 2 gals you should just ph those, ALSO
add 1 tablespoon molasses to the last gallon of water.
ALSO 1 tablespoon molasses drops ph -.3 - -.4 meaning if my water was 7 then it would b 6.6ish.
Thats prob y my plants dont mind i dont check the ph.
Molasses has a shit load of benefits, sugar and micro nutes which look like maybe what your plant is suffering from.