Having the correct pH level is an important part in maximising the amount of nutrient that can be uptaken by the plant. If the pH is consistently incorrect it can lead plant dificiencies and even slower growth. Generally most indoor plant require a pH between 5.5 to 6.5, but it can be more specific depending on growing medium and method.
Caution
This pH down solution is 30% phosphoric acid. Always handle pH up and down with care. If any of these liquids come into contact with your hands or skin, wash immediately and never mix the two of them directly together.