What bonds to Calcium that can then be removed from water?



I'm working on a science project to pull excess calcium from static standing water. Is there a particular element that can bond with the calcium that can then be filtered out of the water? Is there a particular way magnets could be used to remove the calcium? Thank you for your time and any help :)

Oxalates will form percipitates with dissolved Ca2+ ions.  The precipitate could then be filtered.  Also CO32- ions.

I don't think magnets are going to have any effect on the Ca2+ ions in solution.