[cwatkins]

I think you may have fallen victim to old tank syndrome. All of the crap that was trapped in the substrate is throwing you a curve ball.

Since hindsight is 20/20, there's no point in kicking yourself.

I'd do the recommended water changes. Do a big one, and then do smaller ones daily for a week or so.

Try:
-Using ro/di water if you have access to it. Otherwise try filtered (RO) water from a local purified water store. Purified water stores don't usually put water through a DI stage, so the tds may be above zero.
-Water changes are going to be the only way to bring those levels down. A big WC followed by smaller daily WC's for a week won't hurt anything.
-Stop worrying about pH and buffering your tank. Rule #1, ignore your pH (within reason), you'll sleep better at night (okay, maybe not #1, but you get the point). I haven't compensated for pH in over a year. It's too stressful trying to keep up with it. And it changes daily based on your photo period. According to my graphs (click on my signature below), my pH varied from 7.83 to 8.45 in the past 24 hours.