Is there anything special about the Sohum mix or is it just a brand of water-only soil? You could go with an all-in-one dry fertilizer blend for re-amending. At least as a beginner, I've found that is easier than trying to add separate ingredients.
I've been using a mix of KIS Organics nutrient pack and Espoma Tomato Tone at 2-3 cups per 10 gallons, but there are many different brands out there. I see a lot of people on here using Gaia Green 4/4/4 too.
Then replenish the compost/ewc and perlite/whatever you're using for aeration, maybe 1 cup of each per gallon.