You might try some cheaper fixes first. One of the GREAT ways to control pollen is a simple skimmer sock. Frequently, in the spring, it will build up so thickly it looks like yellow spackle--you know, dry wall compound! The sock can be rinsed out and reused for up to a month and are pretty cheap. Gets dust, too, before it gets to your filter. They cost, roughly 4-6 for $10--that's good for 4-6 months!

You can also add a little DE to your filter, just enough (through the skimmer) to make the pressure increase by one pound...but in a sand filter, not a cart.

Why are you changing sand? Unless your sand is gummed up or you have to replace a lateral, you should never need to replace your sand. No reason a working sand filter can't run for 20 or 30 years.