I opened my pool today by myself for the first time. It was incredibly.difficult but I.believe I did it all correctly. After it was all ready, I removed the pressure relief screw in cap and directed the water to waste. It all worked great. When I moved it to filter, I left the cap.off and turned it on. It immediately began whistling and hissing. I didn't even Niger to look at he pressure I just.shut it off. Is there something wrong or should I put the cap back on? I was under the.impression it should stay off till all the air was clearly out. Please answer asap cuz I want my swamp clean by the weekend...if possible.