I had the dolphino easy-set pool 18' x 48" for two summers.
The soup-bowl like sides, not to mention large seams & wrinkles on the bottom, make pool cleaning quite difficult for most vacuums.

I bought a Pool Buster ( by WaterTech inc.). It's like a dust-buster, but goes under water. You can get in the pool with it or attach it to a "real" telescopic pole that you buy at a pool store or hardware store... ( it didn't fit the pole that came with my set).
The Pool Buster is expensive for a donut-pool ... runs about $200usd ( although you could probably find one cheaper on Ebay), but it does an awesome job!

Good Luck!