Grow Mediums Bad soil? Low pH

[Vancho]

The thing is I already suffered from calcium lockup by low pH in two different crops. Using the same soil, one from my zone (Growmix multipro), a mix of perlite, vermiculte, compost and moss peat. Tested de pH: firs crop 4.6-4.8, second crop 4.2-4.6.
Humidity 40-50%, temp 23°C, medium-hard tap water, fertilized with Top-Crop (spanish brand). Lights COB leds white+full spectrum (600w per square meter). Strains from requiem seeds and royal queen seeds.
Also, and I don't know if its important, lights were off very often for multiple blackouts in the area. The timers got delayed as well.
The soil I used gave me no problems for the last 9 crops...
What do you all think?

 

[Bill.de.Cat]

Not sure about that soil, never used it, but my Happy Frog mix I always shoot for a pH of 6 to 6.5 in my water and feed mix and use RO water because my well water is very hard...

 

[Talonxracer]

The soil Ph looks too low. A little dolomite lime will raise the Ph and add some calcium and magnesium.

I would also check your tap water's Ph and EC before adding or doing anything.