HELP! PH is going down despite added higher PH

I need help, all of my plants are suffering from the PH fluctuation. I am growing in coco. every time I give them water the PH is low, then I add some more water with higher PH 6.2, and it keeps going down. so I give them a little water with higher PH but it still keeps going down??
the added water is with nutes.
is it because of the salt build up?
I have been flushing them a couple of times but they keep doing this every time I water. when I flush I give them only water with PH 6.0
I am very very confused, please HELP!


this is a link to my journal

https://www.rollitup.org/grow-journals/72913-first-grow-four-plants.html

Oh growing in coco. No idea.
Sowwy