how to lower soil ph?

Use a lower ph water and it will start to come down.

Using pH adjusted water does not solve soil pH long term. Your readings may come down briefly, but the meter is getting a "false" reading from the pHed water, not the soil. Adjusting the pH in soil is a slow and drawn out process and if your plants seem to be growing fine, I would lock the pH meter in the cupboard and not worry about it again. To change the soil pH long term, you can try adding a handful of dolomite lime or hydrated lime to the top of the pots every10-14 days, and this will over time reduce the pH of the soil permanently. It is not a quick fix, but a stable and permanent solution. In my experience, this can take 3 months or more for the range you are seeking, by which time most plants are generally finished anyhow, making adjustment really quite unnecessary in my opinion. Plants growing in soil are far more forgiving than in other methods, they will take only what they need and as long as you are giving them a complete fertilizer designed for cannabis, they will grow, mature, yield and be just as potent as any other plant of that strain. pH is mostly more critical when growing hydroponically or in coco, DWC etc as the chemical nutrients used in those system are designed to only be available within a certain defined pH range, otherwise they can get "locked up" in the solution and become ineffective/unavailable to the plants and this is why pH is so critical for growers using those cultivation methods. Often trying to solve a perceived imbalance/deficiency, imagined or real, can lead to creating secondary problems bigger than the original perceived problem! If your plants are growing fine and as long as you don't overload them with an imbalanced single type of nutrient/fertilizer, I would suggest doing nothing as your best option. I have been growing in soil for 35+ years and spent a lot of time and effort in the first 10 years trying to get everything "just right" and soon discovered, with sensible feeding and balanced ingredients in my soil mix, it did not make any tangible/quantifiable difference to my plants. For the last 25+ years I have never checked the pH of my soil mix, before, after or during the grow cycle and have had many years of trouble free and pleasing results. 0.5 of a pH range is not going to make one iota of a difference to healthy plants growing in soil and being fed sensibly. Besides, does it matter if your plants have 19.473% THC and not 19. 782%? This is probably the "zone" we are talking about in regards to soil pH and otherwise healthy and well fed plants grown with love and a sensible attitude. God only knows how cannabis has survived for Millenia without perfect soils and perfect conditions, and without any input from humans! Cannabis is a tough and remarkably resilient plant and does not need "Princess Perfect" conditions to grow beautiful and potent flowers. Growing should be about fun and "giving it a go", not an exercise in perfectness! Adding some soil mycorrhizae will really benefit your plants, far more than having exact pH. "Mykos" from Xtreme Gardening gets my vote, it is amazing and with demonstrable effectiveness/results. Since discovering this product, I can not ever imagine growing without it, so impressed am I!! Hope this helps, Organoman.

Water it with pH adjusted water to where you want it. If you use tap water it needs to sit out for 24 hours. Do not drench your soil. Continue to water as normal with the pH adjusted water. You don't want to overwater your plants and kill them. But if there adult plants they can handle a good flush of pH adjusted water. Please know this way lower the nutrients in the medium.