Hi. In case anyone else experiences this problem, it solved itself once we filled this spa with water within 24-48 hours. While we never really discovered what caused the problem in the first place, we suspect that there was air trapped from the jets which hadn't been properly expelled, and that the ongoing pressure of the water on top of it slowly expelled it out as you might if you continued to squeeze an inflatable ring for long enough. Hope this helps anyone else who might experience this problem. Cheers, Mark