anyone know what might be causing this.the spa is a 2000 caldera tahitian.when the number one pump turns off in either first speed or second speed.the water gurgles a lot back through the filter.it does not do this with the number two pump at all.i checked and don't have any visible leaks. i dont think its trapped air.the spa has been up and running for a month now.im worried that when it does this that it is putting some of the contaminants back in to the water from the filter.