If you grow in soil, the optimal pH level for the root zone is between 6.0 and 7.0. However, there is no set number within this range that is “best”. Instead, it can be good to allow for some natural fluctuation within this window to support optimal nutrient uptake.
So, as you adjust, try a slightly different reading each time. You can, for example, adjust your pH to 6.2 for one watering, then 6.6 the next. As long as it stays within 6.0–7.0, you should be fine. Soil is also more forgiving when it comes to pH imbalances, but it can only give so much.
If you grow purely organically—where you do not administer mineral nutrients—pH is less of an issue. If you’re using amended or composted soil with organic matter, the microorganisms within will make the nutrients more available to the roots.
However, most growers using standard potting mixes and mineral nutrients will indeed have to reckon with pH.
Tap water that runs alkaline is filled with mineral salts, things like calcium, magnesium, zinc, normally around 3-400ppm
Alkaline water is drinking water charged with negatively charged ions or "ANIONS" (-).
Cannabis generally like soil to be between 6.0 and 7.0, which is slightly on the acidic side.
At low pH values(acidic), the net charge of most proteins in the mixture is positive (+).
At low pH values in cation exchangers, these positively-charged proteins bind to the negatively-charged matrix as water passes through.
At high pH values(alkaline), the net charge of most proteins is negative, where they bind to the positively-charged matrix in anion exchangers.
Negative repels negative.
By lowering the water to 6.0 you bind all the negative anions to cation sites rendering them repellant as it passes through the medium.
If anything pH down to 7.0, with your medium at 6 it should bounce somewhere around d 6.5 in the middle.
Monitor run off.
If you choose to tap water regularly look to bubble off the chlorine every other watering. Cannabis plants do need it but in trace amount