browning leaf tips bottom of plants

its hard to get a good pick. temps are fairly low and this is only happening at the bottom of the plants. i thuoght it might be nute burn i havent fed them in 10 days, i had sand and traps over the bottom of the pots to clean up a fungus gnat problem. i have been feeding for farms big bloom and tiger bloom. once weekly on thursdays and giving them a clean watering on mondays sence flowering began 6 weeks ago.
temps at night are 65 and day time temps are 75-80. i took deep ph samples of the soil and they came back at 6.5. my PH was dropping before it was almost down to 5.5 so i skipped the last feeding and did a flush with 1tsp of epson salt per gallon and 1tbls of mollases.
i cant tell if its burn or a phospurus deficiency. should i resume nutes at mayby 1/4 to continure to flush? i dont know if they are starving or to full. the bottom leaves all look over watered and i dont know if that is lack of light. the top leaves are fine.
i know its normal for bottom leaves to die off as flowering continues i would like some more opinions if anyone thinks this is going to manafest itself into something farther down the line. mayby its to late into flowering to do anything about it to even affect whats going on. thank you.

oh yeah you can see a gouge in the second pic. catapillars from way back in veg. also in third pick a leaf has lost 3 blades but refuses to let go. and in fourth pick you can see one on the bottom right that is obviously very dead but also refuses to let go. ive had smaller leaves that are green that have fallen off from within the canopy if that helps.