Cool man. Yes, the nutrient pack will reamend A LOT of soil, or you can mix it into your own peat or a light mix (such as the Roots Organic B-2 mix, for example). You add your own perlite, and compost/worm castings and cook it for a week or two. One pack will do about 30+ gallons of soil at full strength, I'd shoot to end up with 40 to 45 gallons so you have 70 to 80% strength.
I've used several nutrient packs and also gave the prebag soil a go. In my opinion, the prebagged mix is slightly too strong for some autos. I believe it is slightly too rich in worm castings. I cut the bag just slightly so it was around 90% strength. My Rainbow Moonstone auto had a little bit of N claw but not too bad. My Amber and Fairy Frost did fine though and were very lush in it.
I would recommend cut it to 80% strength with some peat and perlite, or perhaps some rinsed coco and perlite, and I think it would do most autos great. Also, the prebag mix is like 30% aeration material (they use pumice). I tend to think autos prefer well aerated soil and would probably add some extra perlite anyways, whether you're cutting the soil or not. Another grower I've chatted with feels that 40% aeration is ideal for autos. Anyway, I'll leave that to you to decide but you might want to go ahead and add a little extra perlite to it. Depending on the strains you run, you may or may not see the N toxicity that I did, but I do think you can cut it to 80% and it should be very good. I would not sow directly into that mix though, that is too burly for seedlings. Tier or plug into it after 10-15 days.
I am totally happy and impressed with the plants I grew in this soil, for sure. It performs very well and produces tasty, aromatic and dense buds no problemo, it's so easy. You should go ahead and oh your water though with a non-phosphoric acid product. I use earth juice oh down crystals, which is basically ascorbic acid and will be gentler on the microflora in the soil. The soil can buffer ph for you, but not to an infinite degree. You can just use some cheap test strips though, and just approximate the ph to between 6 and 7 and that would be good enough in my book.
Lastly, the prebag mix worked great but if you need larger volumes of soil, using the nute packs with your own peat, or promix or whatever is much more cost efficient. By a factor of at least 2. You just have to add your own compost/castings, which are not at all expensive. But, per the mixing instructions on the pack, you can choose whether to use compost, or castings, or both. As above, regarding N toxicity, I would recommend half compost and half castings, or slightly favored toward compost. I would not use all castings, again, as some autos are not going to like all that N. Once you have it in the soil, you can't take it out so I'd recommend take care with that and I'd prefer to weakly topdress those castings onto an individual plant if it's truly deficient. I.e. it's easier to add later if needed rather than try to fix it if a plant is getting too much. But just emphasize the compost over castings and they'll do great. I mixed like three batches last summer between 35 and 75% strength. I think close to 75% is great and that 100% is not necessary, but I haven't tested at 100% strength.
I'm looking forward to seeing people try this product line out, I think you will have success with it. Manage the strength of it a little and don't plant directly into it, and ph your water with something gentle and you will get great results with it for sure. I never needed calmag in this soil, even under Led's. It's awesome stuff.
