Personal opinion based on my experience: 8.4 is pretty high. EPA guidelines for tap water has a max of 8.5 (assuming your water is from a municipal source). If you're getting it down to 7.2 or 7.4 then I think you can trust the soil biome to handle it from there. Your next step is very scientific... f-around and find out! Try just getting it to the 7.3 range and see how the plants respond. My tap water is around that and the only thing I do is let it sit for about 24 hours to give the chlorine a chance to get out of there before I put it in the soil. If you really feel like f-ing around and finding out, leave the water as it is when it comes out of the tap and see how things go. Just keep good notes so you remember what worked and what didn't. If it were me, and I had multiple plants that were going to give me way more cannabis than I needed before the end of the next grow, I'd do one with straight tap water and adjust a couple to your 7.2/7.4 and if you really want to experiment, get one down to your 6.8. If you do this, let us know how it goes because that would be awesome!
There are a few ways to keep the top portion of your soil moist without overwetting the bottom of the pot. First of all, it looks like you're using cloth pots which will help a lot. Secondly, before you water, break the top portion of the soil up with your hands so that it's loose and soft. The top layer of soil can often become kind of hard and dry which prevents it from absorbing the water and that causes it to all pass through the top layer and get soaked up by the bottom. Third, when you water, do it in stages about 10-20 minutes apart. I will loosen the soil, slowly add half the water to all the pots, then wait a little bit before adding the second half. This gives that top layer of soil a little time to re-moisten and then really soak up and hold the second half of the water. Soil is kind of like a sponge. If you've ever had a super dry sponge that hasn't been used in a while and run it under the faucet, the water runs right off of it. But if you take a moist sponge and put it under the faucet, it does a much better job of absorbing and holding onto the water.
Also, when it comes to organic soil grows the watering regime is a little different than when using synthetic nutes. More frequent waterings with less water is better than less frequent waterings with more water. This is an article on GWE that I use as a guideline and it works pretty well (you have to scroll about 3/4 of the way down to see it)
https://www.growweedeasy.com/are-cannabis-seedlings-overwatered-how-to-fix
Lastly on your side note: After my seeds germinate (either in a glass of water or between paper towels or a combo of both) I put them in rapid rooters. Once the taproot shows out of the bottom of the rapid rooter, I put them directly into a 7-gallon cloth pot and have never had trouble. Of course, each grow/grower is different but a few things to keep in mind if going directly to the final pot: it may slow them down a day or two for them to get adjusted...but every time you transplant or up-pot, it slows them down as well. However there are two bigger issues to keep an eye on: how hot your soil is and watering practices. You need to make sure that your soil is well cooked and ready to go before putting your seedling into the soil so that the nutrients and soil biome are ready to go. If you haven't cooked your soil enough then the bacteria and fungi won't be ready to provide the nutrients in the soil to your plant and it may suffer as a result. And the real biggie: watering! Watering a small plant in a big pot can be tricky and you can easily under or over-water. If you follow the guidelines in the article above, you should be good. I've also learned that as the plant is little you occasionally need to add a little water around the outside of the pot further from the plant. This helps keep the biome chugging along and makes sure that as your roots grow, the soil is ready to nurture them.
All fun things that make organic growing a slightly different (and to me, more enjoyable) animal than using synthetic nutrients. No right or wrong way, just different!
