It'd be helpful to know more about the pool.
Remember to replace DE when you backflush a DE filter.
sunlove's advice is solid - about the vacuum, the testkit and the CYA. A Taylor K-2006 will be your best pool spend. Find 'em here: How to Get the Right Testkits for your Pool. If you buy through the links, the PoolForum get some cash to keep the lights on.
I think you may have the beginnings of an algae boom - the presence of CC, the FC consumption and the fact the DE filter is clogging quickly are indicators.We'll have a better picture after you can give us chemistry results from your K-2006.