This document specifies a laboratory test method for determining the biocidal/biostatic efficacy of single active substances or combinations thereof used in film preservatives in a coating against algal growth. The document does not apply to coatings not susceptible to algal growth. The test method comprises only active substances for film preservation, not the protection of the substrate itself, e.g. wood, which is dealt with in another standard. The test method is applicable for active substances used for wood and masonry coatings. It is not applicable to marine coatings. Safety, health and environmental aspects are not in the scope of this document. Determination of the performance of film preservatives in coatings by applying ageing procedures is not within the scope of this document.