Glossary · 💧 Water & chemistry
pH
pH measures how acidic or alkaline your water is on a scale of 0–14, with 7 neutral; most community fish are far more sensitive to sudden pH swings than to a stable value slightly off their ideal.
Chasing a "perfect" pH with additives usually causes more harm than good, because it creates the swings fish hate. A stable pH your fish have adjusted to almost always beats a "correct" but unstable one.
pH is closely tied to KH (carbonate hardness), which is what resists pH swings — so if your pH is unstable, look at KH first.