Add one gallon of chlorine to pool water, backwash or clean filter; run filter pump until pool clears.   If pool still does not clear, call a pool professional, as there may be a more serious problem.

You have algae.  Brush plastered walls and green areas with a metal algae brush.   Purchase algicide; follow instructions on container.   Clean filter and add one gallon of chlorine; run filter overnight.   If problem persists, call a pool professional.

Add non-chlorine shock to water and check chlorine level.   If chlorine level is too high, drain pool halfway and add fresh water.   If problem persists, call a pool professional.