I am having the exact same problem and I haven't added any supplements or conditioners to the tank. I have no salt creep in the air line. I'm taking it all apart today (the return box has overflowed three times now over the last 2 weeks). This can't keep happening, I can't leave it on at night or when I leave the house anymore because I don't have any warning when it's going to start to overflow. This seems to happen to several people, there must be some common issue. I just need to know how to fix it, asap.
Thank you for any help.