Just moved in a new home with a pool. From what i can calculate the pool is around 20k gal in ground painted plaster. The filter system has a new Hayward 1 hp max flow pump. The filter on the other hand must be 20+ years old sand filter. I opened it up the other day since it has a band half way around it it looks like it has 50-100lbs of sand in it. I they sales man at the pool store said I must get a new DE filter right away. He said sand filters are no good for an IG pool. I do believe I need a new filter, but do I really have to get a DE filter? Also for the rest of the season (6-7 weeks) I plan on just replaceing 100lbs of sand in the filter, do you think this is enough for this season?