Hello all this may be a dumb question but My wife and I have had this underground pool for about 2 years and it's been hard to keep maintained. I just recently found out that I have a de filter which I have not been adding any de too the time that I have lived at my home. This explains the cloudiness and why it's impossible to keep clean. The owner before me never told me and I'm to dumb to have figured it out long ago. My question is that I have heard that I would need to purchase new filters he says the old ones are now ruined, but would I be able to add de now? The filters have no tears on them and no visible signs of damage that I can see. They are quad 60 de filters and the they cost about $50 each and there are 4 of them. Any advise would be much appreciated.