Abstract: A treatment device for single-stage treatment of a metal object to be treated by at least the steps of pickling and phosphating. The treatment device comprises at least the following: a treatment container for receiving the object to be treated and for receiving a flowable treatment substance; and a pump device for exchanging at least a fraction of the treatment substance. The treatment substance is flowable around at least one part of the object to be treated. The treatment substance comprises a phosphor- or phosphate-containing solution, in particular phosphoric acid. The phosphor- or phosphate-containing solution consists partly of water and partly of a reaction substance, and the reaction substance consists of phosphor or a phosphate and an additional treatment effect-improving substance. The proportion of the phosphor or phosphate in the reaction substance is at least 95%, and the reaction substance does not have a salt acid or sulfuric acid content.