Just an added note about sand filters. Some people say you have to change the sand periodically and that is plain not so. Only under certain situations like converting a Baquagoo pool to chlorine will you gunk one up enough to have to change the sand. Also you don;t need any 'sand treatments' some places try to sell. Just plain filter sand. You do lose a tiny amout each time you backwash but it is almost insignifican. My 300# Hayward has had the same sand for just over 13 years and I should probably throw another 50# bag in the thing. Generally the only time I use the DE trick Watermom mentioned is when I get a bunch of fine silt, dust, or pollen and it does help clean it up faster. They're about as maintenance free as you can get.
Al