As noted previously, chlorine’s main enemy is sunlight. That is where stabilizer comes in. The chemical name of stabilizer is Cyanuric Acid. It’s sometimes abbreviated as “CYA” and may be sold as “conditioner”.
The purpose of adding stabilizer to pool water is to slow the depletion of chlorine due to sunlight. For instance, on a bright sunny day with no stabilizer 85% to 95% of the chlorine could be lost. With the right amount of stabilizer added, this reduction may only be 40% or 50%. In a manner of speaking, the stabilizer “grabs on” to the chlorine, preventing the sun from stealing it away.
Unfortunately, stabilizer also has the side effect of weakening chlorine. Chlorine molecules that are bonded to stabilizer molecules are less effective in killing organisms living in the pool water. So, as stabilizer is added to the water, chlorine levels must also be increased to get the same cleansing effectiveness.
The goal is to establish a balance. Stabilizer is added to protect your chlorine, but not too much, otherwise excessive amounts of chlorine will be needed to keep the water clean.
This is the problem with chlorine tablets that most people use in their pool. The packaging refers to them as “stabilized” chlorine, which means that they contain both chlorine and stabilizer. When first establishing your water balance, both chlorine and stabilizer are needed so these tablets are fine to use. However, when stabilizer gets to the right level, tablets should no longer be used.