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Algae proliferation is an important problem of swimming pool, making it unsightly and ultimately unacceptable to swimmers. Chlorination of the pool seems to inhibit growth of microorganism. However some types of algae can survive the condition and are frequently found (attached on tiles or in suspension). In this study algae samples were collected from a hotel swimming pool and cultured in Bold’s Basal medium. Morphological identification by Direct Microscopic Examination of the culture showed that predominating algae were Oscillatoria, Scenedesmus, Euglena and Phagus. Algae in the culturing bottles were found in 3 zones namely attached on the wall (A), suspended (SS) and settled at the bottom (ST). Ozonation of algae culture with 22.1-141.5 mgO3/L (5-30 min.ozonation time) was found to remove attached and suspended algae. These then settled down to the bottom resulting in an increase in the settled portion. It was noted that ozone consumption of the suspended portion (1.72 mgO3/mgAlgae at 30 min.) was higher than that of the attached portion (0.47 mgO3/mgAlgae at 30 min.) indicating that the former was more resistant to ozone than the latter. In terms of algae type, of the 4 predominating spcies, Euglena sp. was the most resistant
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