What happens if the level of copper is allowed to rise above 0.25 mg/L (ppm)?

High copper levels can be toxic to fish.  Check with the test kit. Un-plug the control panel from the electrical supply if the copper level is over 0.25 mg/L (ppm).  The control panel can be turned back on once the copper level drops below 0.25 mg/L (ppm).  Lower the ionizing dosing level to maintain a copper level of 0.25 mg/L (ppm) or less.  Water changes can also be conducted to reduce the copper to the proper level.