Hey, UB... keep up the great work. Your threads are all in my subscription list, and the first places I go to enjoy some good info and debate. This seemed to be the best place to put my latest spiel..
For various reasons, I've been involved in an off-and-on study of humic acids, composting, and the fundamental nature of "potting soil", all in my spare time of course. As most growers SHOULD know, "potting soils" are about 98% composted wood and sphagnum peat by weight and volume. The other 2% is little bits of this or that, depending whatever marketing tack the manufacturer wants to deploy to sell their bags of rotten wood (ie.. this has "special kelp", mycorrhizal inoculants, or "feeds for 3 months" or whatever).
I got into it because of being repeatedly flamed for using tap water at pH 8.0 without adjusting it down. Why do I do this without a care? Well, the breakdown of natural organic matter creates large amounts of humic substances. "Humic substances" is a HUGE catch-all category of material -- some is fully soluble and easily washed out, some hangs on the soil like a film, other humics hang together in a matrix that agglomerates or separates depending on what is going on around it. Generally, these humic films separate and kick off little bits of organic acid when exposed to alkaline material, like my water. Ergo, I would bet a buck-two-fifty that yes, my water hits the soil surface at 8.0 and by about 1 or 2mm down, is neutralized to 7.0 My plants NEVER see water at 8.0.
So anyway, I just wanted to re-up my humics understanding to be sure of my approach, and then thought it could be useful to others if for no other reason than to eliminate unnecessary steps and stress, and focus on what counts.
Now, there's a helluva world underneath those little tidbits. Here's an article with some insight to it, and how it relates to commercial compost and soil production:
http://jeq.scijournals.org/cgi/content/full/37/4/1608
You don't have to be that great of a scientist to understand it, as dense as it is with references and procedures. The simple output is that commerical soil producers have honed in on the fact that the most beneficial humics are created early in the composting process, and longer and now-outdated composting processes actually strip out beneficial humics. The longer processes may make a "nicer looking" soil, but it has less function to plants as it provides less active and available humics, and more refractory material.
Bottom line: commercial potting soils have a lot of humics, and do not need any assistance with acid buffering (which is what you're doing essentially, when you add vinegar to your water... trying to help your soil do a job it's already well-equipped to do).
One of the primary characteristics of humic substances is an abundant mix of readily available and slow-release carboxylic acids (a multitude of organic acids all carrying the COOH group, including acetic acid.. AKA vinegar). Check this for basic COOH info:
http://en.wikipedia.org/wiki/Carboxylic_acid
So, why aren't potting soils a highly acid intolerable environment for MJ? Because these materials only dissociate into acids in the presence of un-neutralized bases. Otherwise, they remain grouped up and essentially neutral.
Enjoy...