Get rid of it and get a Bubble Magus. I had one of their pumps for an ato - nothing but trouble. The motors are so underpowered they can barely turn the spindle even when lubed to the hilt.
Sounds like your hose could be flat - how old is the santoprene tube? You can try taking the tube out, reversing it 180 degrees, re lubing it, putting it back in, and putting the cover back on. Might have some effect, but if the tube is older than a year or two, it might be so flattened out that you have to replace it.