Increased water changes during summer are essential to counter a triple water quality crisis triggered by high temperatures. First, when water temperatures exceed 30°C, koi metabolism and waste production surge (excretion can increase by over 50%), rapidly decomposing into highly toxic ammonia (levels can triple within 5 days). Second, explosively reproducing algae consume massive amounts of oxygen at night, raising the risk of koi gasping at the surface in the early morning. Third, high evaporation rates concentrate minerals and salts in the water (hardness can increase by 50% or more), creating a stressful, hypertonic environment for the fish, akin to them being in a saline solution.
Increasing the frequency and/or volume of weekly water changes effectively dilutes these accumulated toxins, replenishes oxygen-rich new water (after proper dechlorination), and helps rebalance mineral concentrations. Additionally, more frequent water changes help remove floating algae and organic debris, further stabilizing the pond's ecosystem during this period of heightened biological activity.
