Chances are whether its a particulate cloud or bacterial cloud it will go away in 48-72 hours, tops. You're overfiltering your water so we know that's not the problem. You're extremely zealous on vacuuming other than the above described situation, and water changes for that matter. It's more than normal for a lot of decaying stuff to surface if you're disturbing gravel that hasn't been disturbed in a long time, perhaps even since it was put in the tank. The only difference is wondering whether or not the resulting ''cloud'' is bacteria feeding on the decomposing stuff now in the water column, or just decomposing stuff. I'm willing to bet its a combination of the two. I see no reason to change your water sooner than normal because of clarity or lack thereof unless your params are off again.
You probably didn't screw anything up. :)
If it'd make you more comfy you can probably just turn your filters off for 45 minutes tops if you have some slight aeration, and allow all the crap to settle like some of the forum members do, then re-vaccuum the settled sediment laying on the surface of the gravel.
My biggest word of advice: Go natural. lol
Water params are so much easier to manage with some live plants and driftwood. The wood in my tank acts as a buffer and has gradually brought my PH down from 7.4 to 6.7, where it remains from water changes. This would help your high PH problem to some degree probably, many plants are TERRIFIC at counteracting nitrates, ask PK. I went from changing my water every 4 days to getting by at around just over 2 weeks with my tank ''overstocked'', and nitrates still always remain below 20ppm
I'm only saying this cause there are few members of this forum that I've seen struggle with water params as much as you, (believe me i'm not picking on you, I was there) and it'd be nice to know you're not standing in front of your tank every day pulling your hair saying why god why lol