Flushing sounds like it is going great, but before you go on some pre-chopping cockamamie resin building regimen, I have a few points to input. You have already had multiple rot/mold/and more rot problems, with your water temps, I do not believe it would be wise to let your plants sit in stagnant pools of water for days at a time. Remember that without an airstone or h2o2, you need to maintain a certain water temperature to have a survivable amount of o2 in your water. I believe after about 68 is when your plants start choking without bubbles. If you can keep your temps under that, than that would work great, otherwise we are looking at more possible root rot. I will say almost definite root rot. You know what works, and what is tried and true, so why not keep with it? I thought you did an amazing flush last time, as you noted.
As for 24, 48, or even 96 hours of darkness before chop, there are some serious mold-related problems to consider here as well. Mold loves darkness, mold will spread at a much more rapid rate without UVB to interfere with it's cynical schemes. If you had mold in one room, you have it in all of them. It's sad to say but the spores spread everywhere and infect everything, even if it takes a few weeks to show up. This dark period may take this two week period down to a few days, and it could end up biting you on the drying rack again.
What a dark period really does: Now I have studied this personally for 2 or 3 years now, I have almost always put one plant into darkness before harvesting the whole crop to watch under the microscope and see what happens. Up until recently I have done this, after understanding the effects I only do it as needed. What a extended dark period does is add stress to the plant, and it basically thinks it's already dead, but it still has all the juices flowing. The trichomes do not grow larger, per se, but some swelling may occur; the trichomes are simply maturing at a rapid rate because the plant has been tricked into death, as far as I can tell. I did not notice more trichomes, I did not notice larger trichomes, I noticed a lot more amber trichomes, sometimes by a visual margin of almost 30%. You can see that many trichomes have swelled up, turned amber and cracked open, some have not, some went from clear to milky.
And amber trichomes really glow against the plant. Like Christmas! And the milky trichomes are more visible than the clear ones, so they look more crystallized, but they aren't. And I like the soaring head high I get from some of the clear trichomes, personally. Some people may want more CBD, but I want THC so I can go to space!
In short, if you need to chop at week 7, but you really should have chopped at week 8, you can give it a 24 or 48 hour darkness period to force the plant into it's final stage of maturity, this does not mean you would gain any more weight than you would over a single normal night. At least as far as I can tell, the weight is always within ballpark. I would probably not risk going anything past 48 hours, but I had a grow partner once that went 72 on a White Berry at 6 or 7 weeks, and it came out with less yield because of the early cut, but still smoked fantastic, just like an 8 week crop. This could be a very beneficial practice for SOG growers on a mass scale, growing 7 week blooming plants, that could make more profit by turning them in 6.
And to be honest, the yield on that White Berry was still 2.2 oz on the single plant, and I credit that to the incredible FIM job I did on it, which was the best I'd ever done, and a good job of trimming the scruff out during the first 2 weeks of flower. The original single stock plant pulled 2.7oz, or somewhere close to that, almost 3oz of a 16"-18" plant from in DWC from seed. The White Berry that was put into the 72 hr darkness period was actually a revegged clone of the original from seed I was just talking about. I never do reveg, but this thing was awesome, until it got sick. The clones of the reveg mom all ended up having mold issues and were thrown away until I got more seeds. Which I did!
So, if you ever bother to read all that, I hope it gives you a bit of insight. Because that was a lot of words...
Also on the sub-subject of mold, 16 plants in a 4x4 is asking for trouble, I have my new 4x4 right beside me with 9 OSK and your 2 BD's, which are probably just mom's for now on, because I can't get them to fucking clone for some reason! Arghh! Not to mention they are HUGE. But I have room for more than 12 plants, but with my chance of mold I wont risk it. I think you may want to keep the same mind set. Mold is a common foe between us, we must remain vigilant!
But the rack idea is fantastic.
In other news: Opened up some new bottles of H&G A part and B part the other day. Have had them for 6 months or so, pop them open, and because of the way they are sealed they are fresh as fuck. Now they may not advertise "pH perfect" but it is. I put in the right amounts of everything, according to my PPM meter and my journal of what my plants like, and my pH was a perfect 5.8-5.9 bouncing right between the two, which is PERFECT because the instructions suggest pH 5.89, how the fuck do they get it this accurate? I don't know but it's amazing! I didn't have to do any pH adjusting before adding my tea, or any of my living beneficial additives. Even my old additives are still pH perfect. It has been a few days and pH has risen by 1 point, it now bounces between 5.9 and 6.0, usually by the end of the week it sits between 6.1 and 6.2, pretty snazzy, eh?
The problem is, once these liter bottles start getting old (Because they last forever) they lose this, and pH spins out of control and it takes me like 2 hours to get it stable... Sometimes more. But they stay pretty stable, I have never seen a pH over 6.4 after being ignored for a few days, and that is with the old stuff.
Bad news: The new stuff is watered down.
Good news: I have some extra A&B of their Aqua Flakes formula that was purchased right before the new stuff was put on the shelf, but I've opened it on my last/final DWC grow (not actually final, but as of right now), but still should be pretty stable.
I'm also going to post an article for you tomorrow morning when I'm not so lazy, but it's from the March issue of Maximum Yield, and it perfectly explains your theory of EC and pH being exactly related with your wild pH swings and all the other issues, including mold. "pH perfect" is in the name of the article, in case you get antsy and can't wait. But your original theory was correct about all the problems being related, and this explains why. I certainly learned a lot from it. I learn a lot in the bathroom, lol.
In other news, my SFV comes down in 7 days or less. Chopping a few days shy of 10 weeks, a little later than I wanted too. But I'm working out a completely new schedule, a few complications fucked up the perfect SOG I almost had. They are weaker now so I will have to fight mold, which I saw signs of today. I should actually treat that before I go to bed.... fuuuuck. I forgot I found that horrible powder-spotted leaf.
So that's everything I've been wanting to tell you this week. That, and I am going to have OSK clones soon, and I've seen them flowered out, possibly better than the SFV, by a good bit, I get to smoke it next week, my partner already flowered one out. And I just came up on some fem White Berry and Grape Krush seeds, pick of the litter, all 40 of them. And the Grape Krush is discontinued by DJ Short, and it is AMAZING.
Goodnight, I'm finishing my night with a bowl of Face Off I chopped down last month. Fucking mega dank super-headband effect.