Pool water clarity is dependent on two things: the effectiveness of the filter and the chemical balance in the pool. The pool’s filter provides 85% of the water clarity, and the chemicals used to treat the pool add the other 15%. Chemicals or filters alone cannot keep a pool clear. If the filter media is old it may need replacing. If the pool “balance” is wrong it needs fixing. A D.E. filter may need a manual cleaning, a sand filter may need backwashing or replacement of the sand, and a cartridge filter usually needs a thorough cleaning, but may require replacement of the cartridges. If the pool-water chemistry is okay, it’s time to perform maintenance on the filter.