I just started using the Aquabot Jr this weekend. The bottom of the pool is dirty, and it seems after maybe 5-10min the thing just gets slower and bogged down. I end up shutting it off, cleaning the bag and putting back in every 10min for it to work. Does this seem normal? The bag looks dirty, but it's not full of dirt. Just a grimy substance on the surface on the bag. I figured the Aquabot could handle more than this. Am I doing this wrong?