@north knect here is a little tip mate, for cal/mag deficiencies(which are common with autos) powdered egg shell works wonders for the calcium side of things and molasses does the magnesium.
to use the egg shell just wash out your eggshells and try to remove as much of the inner membrane as you can, then leave them to dry. Once dry use a pestle and mortar to grind them into powder. by grinding them into powder it makes the surface area of the egg shell much greater speeding up absorption. use 2 whole egg shells per 8-10 litres of soil.
eggshell is best used in the beginning soil mix to prevent problems, but if you poke 8 holes around the plant and then drop 1 powdered egg shell into the holes(1 shell shared between the 8)and then take another eggshell and sprinkle on top of the soil, then mix the shell into the top inch of soil, taking care not damage roots. within a week all signs of calcium deficiency will be gone as eggshell is 100% calcium.
to use molasses mix 1 teaspoon of molasses per litre into your normal feed and this will deliver the magnesium you need and as an added bonus it will boost your plant as it uses the natural sugars in it.