VEVOR Faux Rock Cover, Outdoor Fake Rock Well Pump Cover, Realistic Natural Texture, Lightweight & Weather-Resistant Artificial Boulder for Landscaping Garden Yard Décor, Dark Grey, Medium Size

Hello, Interior dimensions: approx 23.6" W × 18.1" D × 13" H (600 × 460 × 330 mm). 18' circumference tank: An 18 ft circumference equals ~5.73 ft (68.8") diameter, which is way larger than the cover’s interior width. It will not fit. Depth: The interior depth is 18.1". Best regards, VEVOR Team