MarineLand Penguin Bio-Wheel Power Aquarium Filter (30-50 Gallon, 200 GPH) $11.72 or Less w/ S&S + Free S&H w/ Prime

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$11.72 when you checkout via Subscribe & Save (or less w/ 5+ subscriptions). Well reviewed w/ 4.4 out of 5 stars by over 28,000 Amazon customers. Lowest price according to a decade of tracking on CCC.
Also available, the 10-20 Gallon, 100 GPH for $8.84 (temporarily out of stock but may still be purchased).