I'm learning more and more about Ca/Mg, and it's been a suspect culprit in some Sick Bay cases I'm thinking,.. Too much is definitely bad, as critical as Ca is for nute uptake/transport, it and Mg can really screw with the uptake of other nutes especially cations,... worse, toxicity symptoms are not exactly glaring, and hard to qualify,... it's a grey area tug-o-war with the LED thing, worse with coco and it's damn CEC bitchiness with Ca/Mg,... there's a fairly fine line between not enough and too much I believe, but what that is I can't point to! for sure, one must review all products for actual content, amount used, and medium content,... make you best guess!
... my thinking is, in soil that's already amended with lime, don't start using Ca-Mg right away,.. coco specific nutes shouldn't add any at all, it's in there already. You water is a factor too, hardness, and medium pH... CaCO3 may be in the water, but may not be in available forms; acidity of course dissolves it to variable degrees,....
I hear you on the N content, some formulation are nitrate based and pretty damn loaded with N, a "hidden" source overlooked sometimes.,...