Is there some reason when I turn on the air blower to the filter that it blows air out the bottom drain with such force that it blows the bottom drain cover off?? I am following the exact instructions that came with the filter for a normal rinse and backwash. This is the first time this has happened, well second as it did it again today. Mike any ideas as I dont want to go swimming anymore to put back the cover... thanks.. It also stirred up all the crap on the bottom of the pond. We also had a hard rain so I had a PH crash as well.. I am crossing my fingers I dont have any dead fish by morning... I salted and did a water change and added some soda.. PH is back to normal but nitrites are still a bit high.. will do another water change tomorrow.. but any clues on why this happened..?