No such thing as a cal-mag deficiency. Calcium and magnesium are two completely different elements with completely different deficiency symptoms. Your plant is lacking neither. This random splotching is typically from pH swinging quickly out of range. Leaf twisting often occurs as well.

6

40 L is about 10.5 gallons.

Recharge has all the correct endo-mycos. Hard water high in calcium will be alkaline. If it’s too alkaline (above 8), you’ll want to lower it to around 6.

Minerals like calcium make water hard. Not chlorine or chloramine. You can’t evaporate calcium.