There are some chemicals that will drop out the calcium as a solid and all you have to do is vac to waste. (TSP or Hydroquest, i believe)
If you had a sand filter, you can also use Zeolite/zeobrite instead of sand, it actually grabs the calcium in a bond, like a softener would, you can then add salt to your filter (system off of course) and let that sit for a bit, then backwash and the calcium will get washed out.