New to coco

[Steveo h]

This is my first grow in coco. 50/50 perlite. Five gallon air pot. Advanced nutes at 75% , micro , grow , bloom. I've been watering every two days using the pot weight method. i've been checking my ph every other feed/water and the last two times after going in at 6.0 it's coming out 4.9 . Can someone help ?

 

[Flockshot]

I am in my first coco grow and hit the same wall. I am using 33% perlite, so I water a little less often at 14 pounds. I flushed with 6.5 till I was getting 6.0 out the bottom and then put 4 quarts each of very mild nutrients. After 2 days they are growing very well and showing the earliest signs of nitrogen yellowing. I will water in 2 more days with regular nutrients.
I think the salt buildup lowers the ph.