There are many things that can cause your pool water to be cloudy, green, and if your water chemicals are balanced properly your water should be crystal clear! One of the biggest problems is people do not keep their PH level and their Chlorine levels proper, thise are the biggest two, most important chemicals to help keep gour water clear.
i recommend one simple thing to make sure your water chemicals are balanced, that is a pool water test kit like the one in the picture above. i am not a fan of the test strips as much as i am these liquid water test kits, they cost more but last a long time and are very accurate and i highly recommend! Also in the paperwork that comes with it shows what you should do when so your pool water can be perfect!!!! Other than keeping your pool water balanced, keep the debris and other crap put of your pool as much as you can for a much cleaner pool and better swimming experience!