That soil mix (humus, manure, lighteners) you were using before was great. Your problem, and the solution to it, is explained in post #10.
Also, adding fertilizer when you are already using a pre-ferted soil with an N value of 0.2, you don't know how much N is left in the soil and may have overdosed. But it could just be the rootbound. Please re-read my posts in this thread, because it's explained carefully.