Just to throw it out there, I bred neos in aquasoil without KH for years. Had more than I knew what to do with. So the word "need" isn't necessarily true.
Curious what was your water source? There may be exceptions based on other factors but as a rule neos generally won't thrive in less than 2kh or so.
I've heard and seen random exceptions to the rule but I don't think that should be taught to beginners.
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