... I'm with Arthur on the RO water, or a blend,... just having some CaCO3 in there to help with pH buffering is the idea,... I blend tap/RO as well, or RO +Ca-Mg (GO CaMg+ 1-0-0) to get about 150ppm,... the whole Ca thing is tricky, it's hard tom spot overload early on, toxicity symptoms usually show as something else getting blocked/poor uptake... rising in-pot pH is another clue,... Ditto for lights, but given the lack of definitive symptoms and the mildness of what i see so far, the lights have been OK,.. usually Ca defc. induced by light blasting shows near the top zone....