A cover arrangement is provided for a launder channel of a clarifier tank. The cover arrangement includes at least one mounting section coupled to the clarifier tank near the launder channel. A plurality of cover panel members are provided, each panel member having a surface and two stiffening flanges located on opposing lateral edges of the surface, where each of the cover panel members further includes a light seal either one of attached to or attached near one of the stiffening flanges. The cover arrangement includes arranging the plurality of cover panels around the clarifier tank over the launder channel such that the light seal attached to or near the outer surface of the stiffening flange of a first panel member among the plurality of panel members abuts against a stiffening flange of an adjacent second panel member among the plurality of panel members.