The medium recipe sounds ok. I like everything but the topsoil. I'd go with something lighter like promix, peat, coco-coir or a combination. I use chunky perlite but the volcanic rock may do the same thing. I also add dolomite lime to sweeten the peat/promix. Check the run-off pH and PPM or EC if you can to see where you're at before you start. Ph should be 6.0-6.7. This is solid data that will tell you more than anyone on the forum ever could.
No doubt that sounds like a very hot mixture you have. I posted a tea recipe from Soma on the forum today. This may be used during flowering to add phosphorus, otherwise the soil should be all the plant needs. Just watch the plants and they will show you if they need more or less of anything.