EDTA测水硬，我用碳酸钙配个800mg/L的标液练着，终点颜色比较难判断，滴不到国标所说的纯蓝色，求大神指教，谢谢????


下图是颜色变化的过程图[img=,690,920]https://ng1.17img.cn/bbsfiles/images/2019/12/201912242041221914_6482_3490514_3.png[/img][img=,690,920]https://ng1.17img.cn/bbsfiles/images/2019/12/201912242041228459_9218_3490514_3.png[/img][img=,690,920]https://ng1.17img.cn/bbsfiles/images/2019/12/201912242041234294_205_3490514_3.png[/img][img=,690,920]https://ng1.17img.cn/bbsfiles/images/2019/12/201912242041239309_9833_3490514_3.png[/img][img=,690,920]https://ng1.17img.cn/bbsfiles/images/2019/12/201912242041263739_744_3490514_3.png[/img]