Abstract: The present invention relates generally to novel water treatment compositions. More particularly, the invention relates to solid water treatment compositions in the form of a water soluble tablet containing at least one halogen source and at least a pH compensating source in a layered tablet in which each of layer is configured to be simultaneously exposed to the water being treated and wherein one layer comprises the halogen source and another layer comprises a pH compensating source. Methods for controlling water biofouling and disinfecting water systems, particularly swimming pools and spas, are disclosed.