If I use pre mixed soil, is it possible to ad feeding to the water for the right ph ? Or better buy a pH down without anything else.

Ph is most essential thing, plants can uptake nutes only at certain values. Off course buy ph meter and ph adjusting liquids.

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

Your diary says its soil based. Soil will manage its own PH well on its own using the microbe life in the soil. I would lower the watering PH down to 6.2-6.5 and call it a day. It looks like your feeding with a salt based formula that does not require breaking down. Soil can hold onto this stuff, less is more, monitor the EC you feeding. even if its not a true soil and soilless the only difference is to get runoff and dispose of it. It also looks like you are feeding from the bottom up. or just letting the runoff wick back into the pot. This can be ok sometimes, but its likely to cause some issues down the road. I would get into the habit of dumping the runoff as most cannabis feeding regimes are heavy and the runoff is filled with excess, this will build up in the soil and cause lockout and ec buildup. then issues with the plant. PH will have different values in the soil like hot and cold spots. its never going to all be the same and that's ok. https://www.stealth-garden.com/wp-content/uploads/2020/11/GHF_NutrientsSchedule_WEB_EN.pdf This is their feeding chart. its not laid out well at all.

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. You want to keep as much of the cal mag from. The water and keep the - charges. 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 amounts.

High Caramelino, It is very simple, you need to adjust the pH from your nutrient solution to pH 6.2 So you need to use a pH down to bring down your water from pH 7.4 to pH 6.2 But you do not need to feed the plant for the first 4 weeks with this all in one soil. But you still need to water with the right pH value, so pH 6.2 In 2-3 weeks you can start to give small dose with nutrients. Like EC 1.2 and bring this value up with EC 0.1 every week till you reach EC 1.8 This should be enough till harvest. Never give more then EC 2.0 to prevent nutrient burning, nutrient lockouts and pH swings. Happy Growing Buddy! 💚