I haven’t used one before but i have just made my first batch of cal-phos from eggshells - as per Emilya’s tutorial. You can either cook them first, for cal-phos or just grind the washed dried shells for a cal supplement. It’s done by fermenting the crushed shells in vinegar for a few weeks.
You can also buy a good quality cal-mg supplement and that would be fine to augment your soil if needed. I can’t advise which brand, I’ve never bought one. Calcium came from seaweed and rock dusts in my own soil grows. @InTheShed can probably recommend a good one.
TBH there should be plenty of all this in your super soil. I’ll have to go back and look at your recipe. BUt really, from memory there should be enough in there. If it were me, making some LABs is something I’d try first before supplementing cal-mag. Give your soil a chance to shine
You can also buy a good quality cal-mg supplement and that would be fine to augment your soil if needed. I can’t advise which brand, I’ve never bought one. Calcium came from seaweed and rock dusts in my own soil grows. @InTheShed can probably recommend a good one.
TBH there should be plenty of all this in your super soil. I’ll have to go back and look at your recipe. BUt really, from memory there should be enough in there. If it were me, making some LABs is something I’d try first before supplementing cal-mag. Give your soil a chance to shine