Creamy and juicy. Calcium in water recipes can help highlight the texture and sweetness of coffees while maintaining clarity at lower ppm. While calcium does a great job of accentuating the fruit notes in coffee, too much can pull in bitterness and drying astringency.
Sweet and complex. If your brew is coming out too one dimensional then magnesium is sure to help with that. This mineral is useful for adding strength and bringing out a wide variety of flavors in your coffee. While the variety of flavor magnesium brings is great, too much can cause coffee to taste muddy or complex to the point that no one particular flavor is easy to identify or pick out. (Mg2+ is what Dr. Hendon refers to as "extremely stick" in relation to Ca2+)
Potassium bicarbonate is like a dial on the perception of acidity of your coffee and it can be quite sensitive. Compared to the hardness ingredients above, even small changes in this ingredient can have a significant effect on your brew. In most coffees potassium creates a sharp but pleasant finish, however, in a coffee with any off flavors this sharpness can often be a bit too intense.
Just like potassium, sodium bicarbonate changes the acidity of your brew in a big way but can also be used to tame bitterness or off flavors. Additionally, in contrast to the sharp finish of potassium, sodium creates a smooth and elegant finish that is very enjoyable. When used to brew a coffee that isn’t bringing a lot to the table in terms of flavor, using only sodium as an alkalinity source can lead to a slightly one dimensional flavor profile.