Crazy soil grow - Black Muffin F1 / Quicklato Sherbet

You can absolutely do it. Treat it like "soil" initially. You are supplementing what already exists exactly the same way as before (i.e. not a full dose of fertilizer early on). However, as the pre-amended nutes are used up, you treat it like a typical soilless medium. You provide 100% of the nutes at around 1.3-1.5EC, give or take, and make sure you consistently get 10% runoff. The runoff ensures what you are adding cannot build up over time. Make sure you have proper drainage chacteristics. In coco base substrate you want 33% perlite or similar. In a 'soil' or sphagnum peat moss based substrate you want at least 50% perlite or similar. This will ensure a proper water:gas mixture and makes overwatering virtually impossible. Though this is what you should do for soil or soilless, either way So, once the nutes in the soil are depleted, fertigate every irrigation with a well-balanced and complete diet at all times. Get 10% runoff or more, religiously to prevent buildup of nutes in substrate. Wait for "enough" dryback and repeat. Simple as that. I suggest you simply go buy a soilless medium. 70/30 Coco+perlite is convenient, but i'd recommend something other than coco. Pro-mix hp or bx are two great options, but you have to add some perlite to it. Poorly processed/buffered coco coir is absolutely dangerous for plants. It will either make them sickly or kill them. It's incredibly bad for the environment due to how much fresh water is needed to fix all the problems that come with coco coir off the tree. If you run into a bad batch it will derail a grow. No such things as "coco" nutrients. That's just a soilless/hydro context. No different than any other soilless context. Coco coir is not magic. It simply absorbs water and holds it for the plant. The only reason 'coco' needs more of something is if it was poorly buffered and as long as it wasn't lethal, that will level out as you fertigate over time -- essentally buffering it on the fly as it reaches equilibrium with your fertilizer. If it's leaching Ca++, that means the manufacturer fucked up big time.