I don't recall what brand/type of jets they used on the Arena (thing is HUGE, isn't it!?) but one of them is either blocked, or has been assembled wrong. The water is being forced back into the air system instead of being drawn in as it should be. First look at all the jets on that air control and see if any of them look obviously different. If not, you may need to take out any removable parts from each jet until you find the one that is wrong or the one which is plugged.
A small piece of scale can block the jet enough to cause this - sometimes in lieu of taking the jets apart I can go around and feel the one which is punk, and then gently probe it with a folded bit of wire (no sharp point) and the water pressure will work out the bit.
HTH
