Brown spots wont stop spreading

I dont know what to do, I feel like my plant is gonna just keep deteriorating. Brown spots showed up on lower leaves, i had some discussions with members who helped me and determined it was likely too much phosphorus, so I flushed both plants well and then gave a light feed afterward to offset flushing all the nutrients out, 1 plant is fine now but the other plant (my biggest one) seems to only be getting worse. I'm at my wits end

Grow info really helps

BobThe420Builder said:

Grow info really helps

Click to expand...

Northern lights autoflower, Ffof mix with around 30% coco, was feeding every second watering using 4 tbsp big bloom, 15ml tiger bloom, 5ml calmag plus in 1 gallon of RO water PHd to 6.3, under a giixer 1000w and a MH ts1000 at about 18 inches from canopy, temp stays typically around 75-80F RH is usually around 45-50

BobThe420Builder said:

Grow info really helps

Click to expand...

I've since lessened that feeding after the flush to 2tbsp big bloom , 8ml tiger bloom and increased calmag to about 8ml