Quik Med PH Up

Many hobbyists test their tap water right away for pH. However, this is not a good indication of your “true” pH. To properly measure your tap water’s pH, pour some tap water into a bucket and place an air stone in the bucket to agitate the surface (to oxygenate the water). Then let this bucket of water sit out for 24 hours. After this, test the water for its pH. It is then a good idea to check it after 48 hours to see if there is any additional change. These values measured after 24-48 hours are an accurate measure of the “true” pH of your tap water.

So, why do you have to leave the water out for 24-48 hours? Carbon dioxide in the water causes the pH to drop. By exposing your tap water to the air and agitating the surface, you are causing a gas exchange at the surface of the water (oxygen goes from the air to the water while carbon dioxide goes from the water to the air). This exchange reduces the amount of carbon dioxide in your water and causes the pH to rise. This pH will be the actual one you will measure in your tank (assuming there are no other objects/chemicals in the tank impacting the pH) as the oxygen/carbon dioxide exchange occurs in your aquarium constantly.