Brunwater calculator work best for me. Work by dilution, ie to lower acidicity,( higher pH values) step by step Do by making 350 ml then dilute to 3500 ml(target) Sanity check: Rinse ph meter with water when pH readings is doubtful. Measure again with tap water, and calibration liquids From experience, initial 350ml is around pH 2.5 or 2.6 When making 3500 as final volume, start by add 80% to 85% of calculated water amount, ie 2800 ml in this case Add the required salts, eg gypsum and calcium chloride before adding more water. Stir to make sure all is dissolved Add 50ml every time to watch how pH values go up ( less acidic) PH starts ~ 4.6 to 4.8 Every 50 to 100 ml lower acidicity by ~0.1(pH values go up 0.1) The trend is not linear,but increase in steps I think ph 5.4 or 5.5 is good enough. My cheap pH meter can have a deviation of 0.2 or maybe more. Double check with ph paper when reaching ~5.0 Tips Constant stirring Read after 15 seconds Cleanse the pH meter ...