Know what the tests mean
pH describes acidity or alkalinity; general hardness reflects dissolved minerals; carbonate hardness influences buffering. They interact with source water and biological processes.
Choose compatible stock
Domestic livebearers often suit harder mineral-rich water, while some wild-form tetras and dwarf cichlids may require softer conditions. Verify the actual species and strain.
Avoid rapid correction
Abrupt pH or hardness changes can be more dangerous than a stable value that is slightly different from a broad online target.
Test source and tank
Compare tap or source water with the aquarium. Evaporation replacement is not a water change and can concentrate minerals.
Use deliberate methods
If water modification is necessary, use repeatable measured mixing and record every batch. Do not add household chemicals based on guesswork.