For things that you can remove (i.e. canopy, filter) use vinegar to help dissolve the calcium. I wouldn't use CLR or another lime remover because they contain chemicals, besides strong acids.
For the tank itself, I guess fishfreak said, maintenance and prevention are probably the best way. You can also possibly use a scraper to try to get it off (don't know if the lime falling into your water would hurt your fish, though). Or use a scrubbing sponge and some elbow grease!