Ok Watermom my cya is 40. have cal-hypo and di-chloro shock. Is one bag enough and which one? BTW there is an Opossum website to tell me all about opossums (like I care). She suggested I tie a towel by the skimmer so they can get out, but she said they are in love with cat food and we have a lady who lives near here who feeds her cats outdoors FOR JOY! Thanks Watermom