Really bad idea. Adding acid to the tank is only going to cause more problems. The pH alteration won't be permanent.
If you want to change it you'll need to find a way to counter pH spike on a more lasting basis. Just as you can add things lik crushed coral or baking soda to raise pH you can also add things to drop it. Peat moss I THINK is one of those things.
How long has the tank been set up? Sometimes whatever is causing the spike will run its course. For instance, adding driftwood can cause the pH to drop but as water changes are done and the tannins leach out of the wood, the pH slowly rises again.
If you just added the substrate I would either tear it down now and start over or give it some time to make sure the results you're seeing a somewhat permanent. Otherwise you'll be playing a see saw game that will get frustrating real quick with you adding chemicals to counteract one thing and then adding more to counteract that.
Remember, in the end, the less crap you add to your water the better of you fish will be.
Tom
