Vessel to use with tablet form bromo-chloro compound. Water flows through the tablets to produce a bromine solution which can then be fed into water cooling systems, ornamental pools, water features and other similar situations where the control of micro-biological organisms are required. This system can be used to prevent growth of biofilms on evaporative and heat exchange surfaces and control planktonic micro- organisms in bulk fluid. Effective in waters up to a pH of 9 and provides a simple and effective control of the biocidal effect of a solid bromine product.