Thank for the answer guys.
The soil ph is between 6.5 - 6.9, and I water at ph 6.5 - 6.0, testing soil ph before watering so that I can adjust the water ph accordingly to the soil.
I'm using fairly small pots, 10 liters, I have a small tent, 80cm x 80cm.
I thought about Calmag as well, just got some, will see what difference it makes.