Multi-purpose water conditioner that acts quickly, safely and easily against almost all pathogens in the pond. The treatment is effective e.g. against bacterial infections (e.g. Columnaris, Aeromonas, Pseudomonas, Erythrodermatitis, dropsy, fin and gill rot), fungi (e.g. Saprolegnia), unicellular skin parasites (e.g. Ichthyobodo, Ichthyophthirius, Chilodonella, Trichodina) and skin and gill worms. The product can also be used to disinfect external wounds and prevents secondary infections.