That tube should suck air if the power is on to the spa. If the power is on and water comes out, you need to find out why.
First, with the power on, pull the filter which goes to the circ pump and see if the water stops coming out and air starts going in. If not, you may have a circ pump which is dying. Call the tech.
You can push a golf tee into the end that has water coming out if it continues even with the filter out, but I would disconnect the ozone generator so it doesn't eat itself up due to lack of airflow.