I had a similar problem but with 50% coco, 40% perlite, and 10% worm castings. I watered all my plants the same, next day I see the LSD looks fried bad. So I started flushing her, the first 2 gallons came out as 7.0. I ran 12 more gallons of water ph'd at 5.5 to get it down to 6.3. Then I ran out of water. I don't like to flush a higher or lower ph through to adjust the ph, personal preference. It kind of sounds like with the really high and low ph'd water you were giving them caused the ph fluctuation. Try flushing water at or very close to what you want your ph to be, no matter how many gallons it takes. If you over water a little it'll be ok as long as the ph is in check.