Do I need to use fertilizer if my soil mixture is ...

So far so good! thanks to your quality soil, you have not run out of K, yet... Potassium deficiency is what you can expect to come after they start to flower. Providing K in dry amendments form is not easy and expensive, especially if you only want K, as you already have *too much* N with the blood meal, and should be *plenty of* P with the bone meal , despite bone meal takes really long time to break down in usable form for the plants. Langbenite is about the only amendment you could add, but like any other amendments it will take a few weeks to start to be absorbed by the roots. Kelp meal would be awesome but not strong enough by itself. Otherwise look for Potassium sulphate. It comes in powder form and a small bag goes a long way. For all these reasons, I recommend Potassium sulphate. Use it right when you receive it, at 400 ppm to water until 3 weeks before harvest.