The relative atomic mass of an element is a weighted average of the masses of the atoms of the isotopes – because if there is much more of one isotope then that will influence the average mass much more than the less abundant isotope will. For example, chlorine has two isotopes: 35Cl and 37Cl.

The number of protons determines an element’s atomic number and is used to distinguish one element from another. Together, the number of protons and the number of neutrons determine an element’s mass number.

Atomic mass is also known as atomic weight. Atomic mass is the weighted average mass of an atom of an element based on the relative natural abundance of that element’s isotopes. The mass number is a count of the total number of protons and neutrons in an atom’s nucleus.

Atomic weight, also referred to as relative atomic mass, is the ratio of the mean mass of the atoms of a chemical element to a certain standard. An isotope is one of two or more species of atoms with different atomic mass numbers (total number of protons + total number of neutrons) of the same chemical element.

35.453 u

Chlorine can be found in abundance in both the Earth’s crust and in ocean water. In the ocean, chlorine is found as part of the compound sodium chloride (NaCl), also known as table salt. In the Earth’s crust, the most common minerals containing chlorine include halite (NaCl), carnallite, and sylvite (KCl).

When chlorine (in any form) is added to water, a weak acid called Hypochlorous acid is produced. It is this acid, not the chlorine, which gives water its ability to oxidize and disinfect. Proper chlorination and filtration give pool water its clear, sparkling appearance. Chlorine exists as a solid, a liquid and a gas.

At a pH of about 5, nearly all the chlorine is present as HOCl, and at pH 8.5, nearly all the chlorine is present as OCl¯. In sanitizing water, hypochlorous acid (HOCl) is 80-100 times more effective as hypochlorite ion (OCl¯).

Water alkalinity and pH are not the same. Water pH measures the amount of hydrogen (acid ions) in the water, whereas water alkalinity is a measure of the carbonate and bicarbonate levels in water. For all water sources, it is the alkalinity that actually determines how much acid to use, not the pH.

You should always adjust the alkalinity first to the 80-100 ppm range then the adjust the pH to the 7.2 to 7.8 range.

muriatic acid

Scaling Buildup on Pool Surfaces Stop using calcium-based disinfectants and keep your pool’s alkalinity between 80 and 110 ppm. Test your levels and carefully add a pool acid, such as muriatic acid to lower pH to below 7.8. If you go too far, add baking soda sparingly to reach the appropriate levels.

Rainwater is known to have acidic properties that can negatively affect your pool water chemistry balance. This can affect anything from the pH balance to alkalinity levels and more. Aside from rainwater falling directly into your pool being a bad thing, something even worse can happen.

Effect on Pool Water pH Since rain is diluting your pool, you may expect that it will reduce the acidity of your pool water. However, all rain in the US is acidic due to pollution, so rain actually decreases your pool’s pH – in other words, the pool water becomes more acidic.

Algae raises the pH of water too Algae consume carbon dioxide, which removes it from solution. In effect, this consumption of CO2 raises the pH, and enough algae can raise the pH of your swimming pool well above 8.2.