Having a heck of a time getting accurate information about replacing our present pool filter system, which is a Hayward ASL series. They're not around any more, and I don't think I'd want one anyway, but what do I want? Conflicting information about the correct size pump to get, whether to buy a filter system with pump or as separate components, which do the best job, use the least energy, last the longest, etc. Any suggestions? We have a 21' round pool, 15,000 gallons I believe.