spotting through out vains end of flower

well everyone unfortunately I am unable to provide pics at this time as my camera is broken and i wont use my phone.
but i am going to give you the run down and see if anyone has any ideas on the problem

First here are the specs
sunshine soil been using liquinex grow 10-10-5 and flower 0-10-10 starting with all grow till flower then 50-50 grow flower mix for 4 weeks then all flower for the last 4 weeks
2-3 feeds then 1 water then repeat every 3-5 days ph is 7.5 it did hit 8 for min (right around start of problem) that is based on a cheap stick in the soil tester and also the pill full of powder stuff
lights are 4 t5s 2 blue 2 yellow and 3 300w equal cfls room is 6x4 and 6 feet tall ceiling plants are 4 feet tall at 6 weeks into flower
temp from 72-82 low-high 250 cfm out 80 cfm in and 2 moving fans

So here is what is happening finding brown spots forming along the vains of all the leaves first with the big older fan leaves then to the smaller sugar leaves as the problem gets worse the
plant shows other symptoms like a little yellowing and curling down of leaves, bud production has slowed. problem started with the weakest strain and then slowly started on the stronger healthier strain have checked for bugs found no signs my thought is potassium deficiency or lock out do to the 8.0 ph thanks for reading and hope to here all your ideas thank you

by the way this is a fictional question needed for a project ;)