Is Halamid when used in water with fish considered as a drug or a biocide?

In Europe, biocides used in aquaculture  are not considered drugs, even when used in the presence of fish. In this case no claim for treatment against a disease or curing of the fish can be made. The function is to reduce pathogen levels in the water. It has been shown that this is preventing diseases and is improving welfare of healthy and diseased animals.