If you have a Petco nearby, you can get bricks of coco coir, the company is Zoo Med, and the brand is "Eco Earth". Stuff works great, but you may want to flush it. I'd recommend a mix of 50% coir, 25% compost mixes(chicken and cow manure, mushroom compost, etc.), and 25% peat moss(for moisture retention). Then use 1 tablespoon of dolomite per gallon of soil, 2 tablespoons bone meal, and 1-2 tablespoons of Espoma Flower Tone(bulb tone works well too). If you can't get the last one it's not the end of the world though. I've been using this mix lately and it's stellar. Actually I use a bit more compost than that, but start with little and add more when it comes to fertilizers you're not used to. Then all you have to do is water with dechlorinated water. That's all it takes to become an organic gardener, and all those soil components are things you can mix together yourself.
I still suspect light leak problems. I know good genes shouldn't care, but a lot of genes that are otherwise good have hermie problems with a little light leak. Also, the time of day the light leak occurs is a big deal. If the leak is closer to either sun up or sun down, it's not as bad, but in the very middle, 6 hours into the night cycle, it's by far the most sensitive. Until you can find more light leak tolerant genetics, you will definitely want future growing to be done with perfect darkness during lights off.
Thanks so much for the recipe !
As for hermies, I'm not sure where that comes from as this plant shows no signs of that. And as for light leaks, I can't say for sure because the only light I see from inside is a diffused glow around the door frame. I put 1x.5 strips around the frame to seal up the gap of the door frame so any light is between the crack and the wooden strips. I run my lights during the daylight hours 7a-7p so it is light for a few hours after the lights go out but, I live alone and don't turn lights on in that room at night.
Is this product similar to what you have suggested?
CocoGro Coir - Bale (makes 65-70 liters) Price: $14.50