How to prevent surface from freezing

here's what to do and it's works just fine . My friend show me this just take a small pump make to go in pond take the hose from it and raise it out of the water about ft so its makes a go move mit on the water .It will be ok to bad she told me after I lost all my koi to the ice had them in a 250 gal. tank got so cold all 4 sides froze befor I KNOW IT .
 
Use a floating de-icer or leave a pump bubbling on a plant shelf to
keep an open area if the pond starts icing over.
 
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