There is a float that is available (like a float in your toilet tank) that monitors the water level in your pond. It opens to let water into your pond from the well, and shuts itself off once the desired level is reached. I've seen them in the Stoney Creek Catalog.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).