How can i solve this problem? The machine was clean we do maintaining general cleaning.. We try severals cleaning chemicals.

<p>Basic Pool Care Tips<br /> <ol> <li>Test chlorine and pH at least 3 times per week. Have a comprehensive water test every 6-8 weeks at your local pool store. There is generally no charge for this test.</li> <li>Operate pool equipment a minimum of 6-8 hours per day during winter months and for 10-12 hours per day during the summer for greatest overall benefit.</li> <li>Brush the pool walls and floor a minimum of once a week.</li> <li>To prevent damage to pool equipment make sure the water level never drops below the opening of the skimmer.</li> <li>Lubricate backwash valve "O" rings on sand and DE filter four times a year. Lubricate pump lid "O" ring periodically with Lube specifically designed for use with swimming pool equipment.<br /><br /><img src="water_1.jpg" /><br /><br /></li> <li>Test pH and add muriatic acid as indicated to maintain pH between 7.4 - 7.8. Never add more than 1 pint of acid at a time and wait at least 1 hour between treatments. Always add muriatic acid by dispersing into pool water opposite the skimmer and disperse as far away from the wall of the pool as you can safely reach. Use care not to drip acid or any chemicals on deck as it will cause deck etching and staining. Do not pour acid over steps, benches, or pool light. Make sure water is circulating.</li> <li>Clean waterline tile with cleaner a minimum of once a month during peak season.</li> <li>One month after initial pool start-up, add stain and scale inhibitor on a regular basis.</li> <li>Always follow manufacturers instructions on product labels.</li> <li><b>NEVER ADD WATER TO CHEMICALS</b> - Add chemicals to water.</li> <li>Always wait one (1) hour between adding different chemicals unless otherwise directed. <ul> <li><b>Filters:</b> <ul> <li><b>Sand Filters:</b> Backwash once per week</li> <li><b>DE Filters:</b> Backwash once filter pressure increases 8-10 psi above your "clean pressure" noted at start-up.</li> <li><b>Cartridge Filters:</b> Need to be taken apart and elements need to be cleaned once filter pressure increases 8-10 psi above your "clean pressure." This cleaning should be done at least a minimum of twice a year.</li></ul></li></ul></li></ol>