At least I think its calcium build up...

There is a lot of build up in the tank, and so it goes out into the toilet so the toilet looks dirty all the time. I've tried sand paper to remove it, but it doesn't work. The only thing that's helped at all was when I had to pour drano down the drain... but it only lasted a few days.

So my question is... what products or how do you remove it from the toilet bowl and tank so that it goes away for awhile?