Just as a note, any Ca++ the soil attracts from the water column will be available to the plant roots, so it's not like the soil is making it unavailable. This does not mean that it isn't a calcium deficiency though.
Generally speaking, most micros do not contain calcium, and most people who do dose GH booster (which contains Calcium, Magnesium, and usually Potassium) will dose it at water change to maintain a certain level on the tank.
With Aquasoil, you really should use RO water and remineralize instead of using tap. Any carbonates in your tap will reduce the soil's ability to lower pH and will eventually deplete it completely.
A very simple option would be to pick up Seachem Equalibrium and dose as it says to. If you don't mind a little extra work, pick up some CaSO4, MgSO4, and K2SO4 instead, and then use a fertilizer calculator such as Zorfox or Rotala butterfly to calculate your dosing of them.
If you have any pictures, that could be helpful in making sure what you are actually seeing is a calcium deficiency