I have 5 plants at two weeks planted in Coast of Maine Stonington Blend which claims to take a plant through to harvest without added nutrients. I don't think I'll take that as gospel so when and if doo you think I should start feeding them and should I add cal mag as well. They are in a 4x4 Grow Tent.
Ken
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I would add in CalMag every watering during Veg just in case as it's really hard to give them too much.
The main thing you have to keep an eye on now is the PH of your water. Try and keep it around 6.5 to 7. If the PH is off, then your plants will not be able to use the nutrients in the soil properly.
Probably give them at least 30 days of just PH balanced water with CalMag. After that try and measure the TDS (PPM or EC) or just keep an eye on them. If the leaf color starts to fade then they are hungry for nutrients.
Have fun!