I lower my ph with limes (not lime, but a lime fruit), squeeze a little juice into a spoon and pick out any pulp..only takes a few drops to lower a gallon. Don't use the pre made lime or lemmon juice since it has sugar added to it.
Whichever you choose, just avoid the stuff with any sodium in it...I made the mistake in the past of using Spa Down, which is sodium bicarbonate and can cause additional problems.