But what about: "Calcium is an antagonist of many heavy metals, as well as phosphorus." So, there is a precipitation of phosphate in water with high calcium and it needs to be added more to maintain the correct N: P ratio?No, not really.
In the end, it's up to you. A good starting point is nitrogen. How much nitrogen do you need? It depends primarily on CO2 & light. If you run high-tech, you'll probably need 10 mg/L NO3-, or maybe even more. In low-tech, see my chart above.
Nitrogen to phosphorus ratio is known, it should be around 16 : 1 [on molar basis]. Similarly, potassium to nitrogen is also a given: 1 : 4 [molar]. There may be more potassium, but not less.
As for K, Mg and Ca, there should be several times more Ca & Mg than K. Mg to Ca ratio is less important than people often believe. Only in hard waters, sometimes there's too much calcium and too little magnesium. If that is the case, you should add magnesium. A ratio 1 : 2 [again, molar] for Mg : Ca is ideal, 1 : 5 still acceptable for most plants.
I understand and take into account the ratio of Nitrogen and Potassium, but what are the ratios of elements with Calcium? So far, it turns out that there is nothing terrible in the fact that there is a lot of it, but in practice I see that plants do not feel well in water with a lot of Calcium…
On the other hand, I have a lot of carbonates, perhaps they are the reason for the poor growth of plants..