What is pH?

PH is a measure of the acidity or alkalinity of a solution, in this case, your aquarium water. More specifically, pH is the measure of the concentration of hydrogen atoms in the water (H+). This measure is stated on a logarithmic scale ranging from 0 (being acidic) to 14 (being alkaline). A logarithmic scale means that a change of one on the scale represents a tenfold change (ie. pH4 is 10 times more acidic than pH5). A pH measure of 7 is neutral.

Goldfish can tolerate a wide range of pH levels, ranging between 6.0 - 8.0. The ideal pH parameter for goldfish is generally accepted as around 7.2 pH, but I feel that the ideal pH parameter for your goldfish is whatever pH level your tap water is naturally. Like most other water parameters, it is important that you maintain a stable environment for your goldfish. Sudden swings in pH levels are harmful, and can be deadly, for your goldfish. Goldfish can thrive in a wide range of pH levels, as long as they are acclimated to it first. It is unadvisable to use chemicals and other additives to artificially raise or lower the pH level of your aquarium water, as the potential disaster of pH swings far outweigh any benefit.

The pH levels of your aquarium drops slowly over time as acids are produced by fish waste, respiration, and other organic activities within your aquarium. Regular water maintenance helps to stabilize the pH in your aquarium. (to the natural pH of your tap water)

Note also that higher pH levels fosters higher ratios of free ammonia to ammonium. High ammonia levels coupled with high pH levels are a deadly combination for your aquarium community.