Cal/Mag deficiencies??

Ok, well it looks like summer is here and my plants are all re-potted and look to be thriving. Only problem is cats getting to the lower leaves and what I believe to be a cal/mag deficiency, getting some rust spots between the veins on some of the lower fan leaves. This only seems to be affecting my seedlings, the clones don't seem to be having this problem but all are in pretty much the same soil base(mg soil/generic potting soil, lava rock, manure compost and worm castings all mixed together) although four plants are in generic potting soil only. According to the MMJ Manual by Rosenthal the cal/mag deficiencies aren't a real problem other then the symptoms they don't seem to harm the plant but this doesn't make me feel any better about things because I don't want to see the symptoms.

Will I have to keep adding cal/mag to my watering or is there something I can get that will linger in the soil so I don't have to keep adding it? I'm using nature valley vitamins that I take myself so is there any harm if I give a bit too much to the plants? With the crazy weather we have here it's probably going to take a week to be able to notice any difference, they got battered around pretty good by the wind/rain/hail but looks like we will have sun from now on.