A pump used to purify water in a pool, pond, or tank:the pool comes with a filter pump...
It's important to make sure the filter pump and heater you do have are the right size for the job.
I have a 150-gallon tank with filter pumps.
Throw in a fence, a heater, a motorized cover, and a filter pump that runs 24/7, and I've spent tens of thousands of dollars to surround myself with water.