Okay, your pots are probably big enough. Remember a gallon of dirt for each foot of main stem. A bushy plant needs a bit of a bigger pot. You can always slip a tub of dirt under there, put the plant, pot and all, on the surface, and cut the bottom of the pot right off like BOG used to do with his monsters.
I suggested the cheap soilless because you are already approaching harvest and it's time for something inexpensive and unfertilized.
Always add your calmag FIRST because you are just using it to make 'fake tap water' of 300ppm.
You can use humic acid supplements in your fert solution too, modestly; add them aafter the calmag but check the pH right before watering. I just like to flush with it personally, because really good quality nutrients contain it anyway- the Canna line, BioBizz TopMax, and Pure Blend Pro all have it as a component.