OK, met with the sellers with the wife. Talked for over 2 hours about the home and pool. I found out it is 25,000 Gallons. It does have the Nature2 unit installed, but she said it does NOT have the cartridge installed in it. She said it was starting to stain the pool skimmers, so she removed it. They used a basic kit to check the water condition. She was very helpful and even gave me detail instructions on how she did the maintenance and cleaning of the pool. I should be able to pickup where she left off after closing (2 more weeks!). They fixed the cleaner pump which had a leak in the pump seal. She also showed me how to run the timers and feature pump for the waterfall and sprayers. I will upload pictures after closing. Thanks for everyone's help.