Just as an aside here, zebras could care less if you have them at a lower pH. I've kept them in Kansas City tap water at 8.6 pH and 17 degrees kH and over 25 degrees gH. They do just fine, as long as the ammonia level is kept nonexistent with adequate filtration. Mine first started spawning here with my tap water at 7.8 pH, kH 7 degrees, gH 9 degrees. Messing with the pH is only going to cause fluctuations that are far more stressful, IMO. With water that's nice and hard like yours, it's easy to vary the TDS rapidly to simulate a rainy season. I've actually had to figure out ways to get the water harder here and still get the fluctuation I need to get them started. At least it's finally working again.
I guess what I'm trying to say is that people put so much work into exactly matching the conditions they're found in, when actually, those conditions fluctuate through the year when collecting isn't feasible and conditions aren't documented. Harder water does NOT stress the fish and they condition well in it. It's nice and stable and safe for them. Screwing around with changing the conditions can make it potentially unsafe, so why bother?
Barbie