Adjusting PH issue

So, re-callibrate pen and test in a known pH and make sure equipment is not malfunctioning. This would probably cause some sort of issues in plant if it were way off. So, you'd have an inkling if this is the case before you check. Check if your local water is using chloramine or not? if so, sitting it out for 24+ hours is doing nothing but stagnating your water. Chloramine does not gas off like chlorine. Also, light breaks down chlorine fast. you probably could leave it in the sun and not need 24h to accomplish same thing. No idea how fast, but wouldn't take too long at such low levels plus normal gassingn off of Cl-. also, stop leaving it out for 24+ hours even if it is chlorine in use. This will do more harm than good. The amount of chlorine in tap water will never build up, even with bad watering habits, over 4-5 months. Maybe with a house plant or a mother plant it is more of a concern over multiple years in same pot, but a consistent runoff when fertigated/irrigated will avoid this potential problem too. (don't use rain water, either,... just adding air pollution to plants, lol... "natural" does not equate to "better", it is completely random wether 'natural' is better or not and often a total perception error to start.) if it comes out at 7.2, it shouldn't need much, and if using same acid, the amount needed should not change. Re-check tap ph. I've seen mine swing from 8.4 to 7.0 in past. The acid has lost its "strength" if you need more to move the needle the same amount as before. Contamination or just possibly naturally breaking down over time, i don't know. Doesn't matter how.. if it requires more than the past with same starting pH, that means it has less active H+, therefore a more neutral pH than before -> more needed for same effect Stop buying branded ph up down bottles.. these are simple every day acids and bases. One acid is not more robust to ph drift than another. that is going to happen in any unbuffered solution -- if you use soiless/hydro nutes this is a bad sign if ph-drift occurs.. that's a shit-ass manufacturer that doesn't know what they are doing. Also, if soilless/hydro context, a proper fertilizer should ph-balance and buffer for you.. this shouldnt be needed except for organic or "soil" nutes. Save money. But white distilled vineager 5%, which likely exists in your house already. Start using that. I doubt you need more than 1-1.5mL per gallon, if at 7.2 to start. A 3gallon jug is a few dollars and will last years. citric acid is another good option. you can even use some that provide nutrients, but i prefer to use acids that don't require me to re-balance my nutes. nutes are all about the "right" amount, not "more" of any 1 thing. Don't let someone tell you vinegar is more prone to ph drift.. that's nonsense.. Drift happens because a solution is not buffered properly. a good quality hydro/soilless nutrient lineup should do this for you... those that don't have failed as manufactuers... soil nutes are their own animal in this regard for various reasons - just part of the fun of soil grows, lol. the microbes should control pH in that context, but have physical limitations in that regard. If drift can occur, it does not matter which acid you use. the same forces are at play in both situations, despite common perceptions on the matter.