当天然水中的碱度＜硬度时，下列说法中错误的是（）。
A.天然水中〔Ca2＋〕＋〔Mg2＋〕＞〔HCO3－〕
B.水中既有碳酸盐硬度，又有非碳酸盐硬度，而无负硬度
C.水中必有永久硬度存在，无钠盐碱度
D.碳酸盐硬度＝碱度，非碳酸盐硬度＝硬度－碱度
E.水中的总碱度＝暂时硬度，永久硬度＝总硬度－总碱度
F.水中没有非碳酸盐硬度，也没有负硬度，只有碳酸盐硬度存在
参考答案：F
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