I'll probably get blasted but I cleaned mine with a water and muratic acid mix. It totally disolves the calcium build up then you just rinse it out. When the acid is rinsed out with tap water. I'll brush it down to take off any residual slime said:
Man, you are braver than me, We use that stuff at work to cleane concrete off our concrete pumps, I cant stand to use it on the clock, while getting paid to use it much less at my home or even the thought of useing it on my tank in anyway,shape,form or fashion, noway. Just my thoughts.