Bomber's right ... my rock wasn't cooked as part of my `removing substrate' process.
I have since taken some out to cook and put already cooked stuff in ... but that is probably now 1/3 [?] of the rock - and in late summer when I had the issues maybe 1/10 of the rock.
IMO, my rock shed `strongly' for 3 or 4 months. Bi weekly piles of substrate to siphon up - could have done it daily [and did for periods]. It blew me away. Months of crap, with a macro-algae boom [particulate detritus IMO on the rock] right near the end.
True to form, though ... as things got cleaner and cleaner the algae slowly lost color and withered away. It took more patience than I wanted, but yet even the red hair small spot I've had for a year is gone. I'd cook the rocks more next time ... but yet having gone thru the process without losing a coral, I'll take the slow process to get `here now'

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And I was removing a 1/2" or less bed of 1-3mm + sand ... not a true DSB at all, not even close. I'm probably not the best example, given that.
I'd agree about the flow. There's a `mojo' to it for a 58g tank IMO ... it's a long way up to that overflow.
It's easy to focus on randomization, plumbing, or gph when -> `its how you use it' is the effective part to focus on.
I run less flow than I did at one time, and am happier with what the water is doing ... though I know I'm still at the excessive end of flow. I prefer the windblown look, I guess.
It's so hard to explain flow, and I don't feel like I have it down yet. Best way is to say that while I still have about the same amount collecting on the bottom [in the same two spots it always collects] .... but after my flow-scape-change only in one spot of my LR do I get significant amounts of detritus when I turkeybaste the LR. Everywhere else is clean, with minimal to no detritus there to disturb.
I'm assuming that stuff now makes it to the overflow, and is that particulate crud in the bottom of my skimmate container. I guess that's the best way to try to explain what's different with my flow - the rocks aren't collecting debris in any significant extent.