You really do need to invest in a kit that has both GH and KH tests, API makes one. Your GH and KH should be at least 5, if I remember right, in order for there to be enough of the proper chemicals (including calcium, which is your KH number) in the water to keep shells hard. Ph should also be no lower than 7 as acid water helps to break down their shells. The water is as important maybe more so than supplimenting food. Don't get me wrong food or calcium blocks are good but you need proper water hardness to keep them healthy.