Chlorine from various sources such as calcium or sodium hypochlorite (bleach) has been used for decades as a germicide to control microbes (bacteria and fungi) in flower holding solutions.
Probably the most prevalent use of chlorine is at grower level where it is added to water either alone or in combination with other ingredients. The effectiveness of such solutions was investigated by a team of researchers (Xie, Joyce, Irving, and Eyre, 2007, Postharvest Biology and Technology) and their findings are summarised here.
To begin with, the researchers used the sodium salt of dichloroisocyanuric acid (DICA) as the chlorine source in their tests. For simplicity, bleach is described in the writings presented below, as it is better known than DICA and similar results can be expected.
When bleach is mixed with water, it breaks down into various components that have different capacities in controlling microbes. A simple, inexpensive and fast test to determine if a bleach solution is effective in controlling microbes is measuring the free chlorine, which should be in the 5-10 ppm range. Free chlorine test kits are available from many sources including swimming pool supply companies.