Hello, I hope this is being posted in the correct location. I have a Pondmaster 4800 hydrive pump. The pump stopped pumping, I soaked it in vinegar for 10 minutes and it ran for a few days. It stopped and I pulled it again. I soaked it in vinegar for 24 hours and now I am trying to remove the impeller to check it out. I am having trouble removing the impeller. The impeller pulls off the metal shaft but I am at a loss... How do I pull off the plastic cover that keeps the shaft and the rest of the impeller enclosed in the filter. I have a backup pump so the fish are safe but I would really like to service this unit for backup purposes. Thanks for your ideas.