The short answer
Match pH to your fish, change it slowly, and don’t chase a number. Most community fish adapt to a wide range of pH, and stability matters far more than hitting a textbook value. If you truly need to adjust it — usually only for specialist species or breeding — do it gradually over days using natural methods, and never dose fast-acting “pH up/down” bottles that cause dangerous swings.
First, decide if you even need to
Test your tap and tank pH with a liquid test kit and compare it to what your fish actually need. In most cases the answer is to leave it alone: fish sold as community species are typically farm-raised in average water and cope fine. Chasing a “perfect” pH usually causes more harm than the original reading. See our water testing hub for how to read the results.
To lower pH (make it more acidic)
- Driftwood and botanicals (leaf litter, alder cones) release tannins that gently soften and acidify water — the natural, stable approach.
- Peat filtration or RO water blended with tap water lowers both pH and hardness for soft-water species.
- Go slowly — aim for no more than a small change per day.
To raise pH (make it more alkaline)
- Crushed coral or aragonite in the substrate or filter slowly raises pH and KH, adding stability.
- Limestone or shell-based hardscape has the same effect for fish that like harder, alkaline water.
Change it slowly
Whatever the direction, adjust across days, not minutes, and keep an eye on fish behaviour. Steady partial water changes with consistent source water keep pH stable in the first place — see how to do a water change and our maintenance guides. Also confirm your water is dechlorinated first: is tap water safe for fish?