Yes, but what you are not understanding is that plants don't take up Calcium Carbonate, even when crushed up and watered into the soil. It takes time to be broken down into Calcium ions which can be taken up by the plant's roots. Calcium Carbonate is water soluble but plants can't absorb it, so that is NOT true that "anything water soluble acts quickly".
ok first of all your right in a sense, it does need to be broken down..thats what your doing by making it water soluble..
grab 2 cups of bat guano powder, mix it in a gal jug and pour..you will fry that plant over night..so thats slowly?
i think not.
second..your not feeding the plantz roots man, for feeding the biology in the soil etc.
they in turn feed your roots..
so your not breaking it down for your roots at all..
by making it powder, then breaking it down with water(water soluble) it will have some instant results..nothing major..
but if his plantz already cal def..well, its going to take at least a min of a week for it to even come out of it or show signs of cure anyway..so how can you say that you "know" shells etc(the most calcium riddle shit on the planet! made from calcuim) can not simply be broken down?
honestly i think the word your looking for is chelated. and hes looking for a free alternative correct? or did i read it wrong?
if he had money i would of told him to get superthrive and call it a day. but thats just me..
lets agree to disagree.
cheers