At least you have somewhere to start. I killed 3 plants already and my 40 day old needs calcium. In my young ignorance I've been feeding her bottled water for far to long. Powdered some egg shells for the soil and switched to ph'd tap water, I hear it has traces of calcium in it.
I feed rainwater as much as I can, but I get 35 inches a year on average. Bottled water is fine and doesn't have chlorine, chloramine and hexafluorosilic acid [fluoride derived from synthetic potassium fertilizer] in it, that's nice.
Are aerating your tap water or letting it sit to evaporate out the chlorine? or maybe you are lucky and don't have it added to your system, but now chloramine is being added in its place.
Calcium deficiencies can certainly be helped by top dressing with powdered kelp [although I use stinging nettle...land kelp]
My brother in law actually made me some calcium phosphate this year and I need to make more, I have the recipe which he used [have to dig it out]
but basically you roast the eggshells and then soak them in vinegar, the stuff works awesome...[I don't know why I waited so long to make more, lol,]
Bone meal is another option for calcium, takes a while, but a nice pre-cooked soil before you plant should be nice and supplemented.
Lastly, if you really have been following this thread, I make my own ferts where I can. I harvest a bunch of plants and ferment them to "tea" and mix with water.
Plants I harvest that have lots of calcium include:
Dynamic Accumulators of Nutrients for Composting
horsetails
stinging nettle
comfrey [although I pick something called Houndstongue, even bigger and leafier but still in the Borage family]
wild savory [mint family]
parsley