I've searched the site, and found a few "sort of" related topics, but none quite like mine - so sorry if already asked and answered.
I have recently had my pool installed, and against my pool builders advice, I bought my Pentair VS 011018 pump (for $900 less than he was asking) off Amazon in February. Fast forward to the install, and running the pump (this past week). Any time I run the pump at lower speeds (1250 - 2350), my basket quickly drains down to half full, and my Hayward 72 SQ FT DE Filter starts taking on air. I asked the guy who installed the equipment if that was normal, and he said no - and took a look. He told me that I must have got a bad pump, and that's why I should have bought from them. I'm a little cautious as to his diagnosis, as he allowed a large quantity of DE to backflow into the pool while gluing some joints he missed during the install.
First - is this normal to have a basket run half full at lower speeds? Second, if not, would lube on the "O" ring resolve this? What would be some other suggestions?