leaf burn Ph or overfert?

using ocean forest organic soil
reverse osmosis water
1000 watt light w/fan (produces no heat)
80 degrees in room
***been using the "all in one" kick ass soil. A guy at the grow store said to use 1/4 tsp nutes in my water because R/O is soooo clean it actually sucks the nutes from the roots (???).

My PH is weird...I'll measure it out of the R/O filter which says @8. I only put 1/8-1/4 tsp PH lower per gallon and then retest it to find it's dropped to 5-6!?!?!?. Anyone ever heard of that?

I have Aussie Blues from "Amsterdam seeds" site and 3 (out of 30) have began to show some signs of burning on the lower big leaves. All the rest are fine. I did water them once with ph at 4 (yes, I'm a dumb ass) but now am back to 6-7. Any help? Don't know if I should stop putting nutes into the water due to it already being in the soil or keep the PH up a little bit? Sorry about the book!!!

pics...........

yep............

Ocean forest is good soil and you won't need any nutes for the first 3-4 weeks. Use something high in nitrogen as it will use alot while filling out in veg. Phing RO water will swing quickly as there is nothing in it for the up or down to effect except for the water. It's when you add all the nutes you will find the stronger the mix the more it will take to move the ph. If your in soil you want it around 6-6.5 while watering, this will keep your soil ph around 6.8-7.... This is what can happen to your plants if you don't ph them https://www.rollitup.org/marijuana-plant-problems/48750-way-much-ph-up.html Good luck.....

as the soil dries the ph should go up a bit, but like the last guy said, water with the nutes at a ph of 6-6.5 and you should be fine there.