Abstract: A method for washing one or more tanks for containing aquatic animals includes inserting one or more tanks for aquatic animals to be washed into a washing chamber of a washing apparatus. A washing solution is supplied to the washing chamber and comprises an alkaline detergent in combination with hydrogen peroxide. The alkaline detergent is free from surfactants, phosphates and chlorine. A neutralizing agent is supplied to the washing chamber and also is free from surfactants, phosphates and chlorine, to re-establish a desired pH of the residual washing solution in the washing chamber.