Why It's Critical to Ensure No Chlorine Enters Koi Ponds

Koi pond owners must be vigilant in preventing any chlorine from entering the sensitive aquatic environment that healthy koi require. Here's why chlorine can quickly become deadly to precious koi fish.

 

Koi produce a protective layer of mucus on their skin and scales that serves as an initial barrier against toxins and dangerous pathogens. However, chlorine ruthlessly destroys this crucial mucus covering, leaving koi susceptible to a host of bacterial, viral, fungal and parasitic attacks.

Once the mucus coating has been stripped away, dissolved chlorine immediately targets koi gill tissue. Even low concentrations burn and destroy delicate gill filaments that allow for oxygen exchange. This leaves koi literally gasping for breath.

The nitrification process carried out by beneficial bacteria in biological filters is also devastated by chlorine exposure. Chlorine will rapidly kill off massive colonies of Nitrosomonas and Nitrobacter bacteria that convert ammonia and nitrites into less toxic nitrates.

Over time, chlorine bonds with ammonia that is perpetually excreted by koi to form chloramines. Chloramines are vastly more stable than lone chlorine molecules, taking weeks or months to eventually break down or dissipate rather than hours or days. Prolonged chloramine exposure has been implicated in koi cancers and reproductive issues.