Lil Help, spots

Brown spots,

coco, PHperfect AN nutes, RO water, 40days in flower,

15ml of cal-mag
15ml of micro, grow, bloom each per gallon water I use currently. (calls for 16ml per at this stage )

runoff 1780ppms,

ok, think its potassium def.

didnt start till flower,

think sodium buildup personally, IDK

Should I flush? If so, how in Coco. I use PH perfect for a reason, because my PH meter is shit. Id imagin I still have to PH water to 5.8?