Hayward recommended this filter for my inground 22,000 gal pool. I am only getting 2 months between total cleanings. This seems too much. The back charge does not buy me anything. The filter when opened shows very little algae and the tubes rinse to white with plain water. The pump is a 1 hp, but stops pumping water through after 7-8 weeks. I rinse, drain, recharge de and it works great for 2 months. What am I missing here? The pool is not used very much at all, and chlorine and shock is done regularly. Help.