Algicidal and fungicidal preservative with Alternaria effectiveness

The present application describes a preservative which comprises a) at least one compound from the class of the pyrithiones which are active against Alternaria and b) at least one compound from the class of the algicidally active triazines and/or c) at least one compound from the classes of the fungicidally active benzimidazoles or thiophenes and customary auxiliaries, where, in the absence of benzimidazole or thiophene, an additional presence of algicidal urea compounds or biocidal hydrolysable polymeric resins is excluded.