I have the same problem and found the best tool to be a pumice stone. You basically scrape the calcium off with the stone. Make sure you get one specifically for pool use and it will last a long time and go far. It isn't easy though. It takes a LOT of elbow grease and you can expect to spend maybe 30 minutes per linear foot, depending of course on how heavy the buildup is. I personally gave up on my pool after putting hours of work in and barely making any progress. It will also cloud up your water with calcium and pumice particles, which should settle eventually. The best time to clean is probably before you plan to drain the pool, so you can flush out all the bits released. Also beware if you have glazed tile as pumice can scratch it.
You can also try spraying the buildup with a mixture of muriatic acid and water. This works best for faint stains rather than heavy buildup. Be extremely careful and follow all safety precautions when working with acid. Also be careful as you can damage your plaster. If your pool is in need of acid to balance the water, this will kill two birds with one stone.
Finally, you can pay someone to do it, but it isn't cheap!
The best recommendation is to prevent it in the first place by keeping LSI balanced--there is tons of reading material on this and you can find calculators online.
