Paul, let me first welcome you to the forum, best thing you could have done is comming here and finding out what 'proper' pool maintenance is!! There's no problem with installing a SWG (SWCG) on an existing pool, unless there's not enough room for the unit on the filtration system. Take a good read on the SWG section, you can use the 'search' function to get more specific info, there have always been posts about 'which is best' - read them and discover for yourself which unit will do what you need. I hope this answers your question, at least partly. Good luck, however you handle this!!