PH 7 in 1 Gallon Pot HELP

how much PH down 75% do i need in 1 liter of water to lower my soils PH to 6. I am growing in miracle grow, and can i also add CAL-MAG PLUS in the water to?

your not going to lower the soil ph that fast, and its not a good idea if you could. 7.0 is fine imo. i would just ph your water to 6.5 if your water is high. the thing you need to be careful about with mg and other time release ferts is getting the soil too wet. if the soil is new i would be careful about adding more nutes for a while.

my plant is locking out nutes and is dying it also has purple stems so its cal deficient

you shure it's lockout from ph? the most common prob ppl have with mg is from overwatering. the time relese ferts will disolve too fast and burn the plants not to mention the normal root probs. 6.5 is ideal for soil but 7 is still ok.

https://www.rollitup.org/marijuana-plant-problems/488004-guide-nutrient-deficiency-toxicity.html
https://www.rollitup.org/marijuana-plant-problems/150004-plant-moisture-stress-symptoms-solutions.html
these threads are def worth a read if your having probs.
if you need help figuring out whats wrong ppl will need photos +
age of plants, soil type,watering sched, lights, temp, any nutes... the more info, the more helpfull people can be. hth