Tap water and PH rebound

well i have grown in coco/perlite in regular pots with lucas formula and tap water for years

i wanted a soiless medium that is easyer to work with and adjust PH so i am trying pure perlite hempy buckets

im useing lucas formula and same tap water as i did in coco

and it seems i have nute problems all the lower leaves are turning yellow then drying and dropping

i know its not realy a nutes issue i flushed with 4 gallons of nute salution to be shur.

i am adding a 1/4 tsp of GH PH down to each gallon of ferts and it gets it to 5.8

the only cause of this i can think of the water is high PH buffered from the tap, and since the coco was a buffer when i used it befor i had no problems, but now im in perlite wich has no buffer, so i think thats wy it is a PH rebound inside the hempy bucket after i water

is the only answer to buy a R/O filter?

i dont know what to do is there anything i can add to my ferts mix to buffer the PH were i set it, so it wont rise back up so fast and starve the plants

and maby i cant use pure perlite with tap water, maby i will have t oadd somthign as a buffer next time i grow,

what do you gusy think any ideas

 

out of the tap water is 7.6 PH and 190 ppm

i realy am puzzled about this, like i said used same watre and nutes for my coco grows

and yes i am useing GH lucas formula after nutes i add 1/4 tsp of PH down and it gets it to 5.8

i know my nute solution is right on were it should be, but for sum reason the lower leaves are turning yellow and dieing

the only thing i can think of the the PH rebounds after i water,

for some reason when i used coco my PH was always droping to super acidic lvls, even i with this water. in coco my runoff would be 4.0 alot of times and i would have to flush

thats wy i went 100% perlite, the coco just always held to much PH and ppm i wanted something that can be flushed easlyly and corrected easy

but for some reason im loosing lower leaves at an alarming rate, PH rebound is my only guess,
i know the nutes are there so it cant me lack of nutes, and the plants are eating of its lower leaves leads me to think its PH, but like i said the nutes go in at 5.8

is a R/O filter the only way to get rid of Carbonate hardness. can u use an active charcoal filter??

i read that Carbonate hardness (KH) is what makes tap water rebound

i just dont understand wy the water would work fine for plants in pots with coco but not in buckets with perlite