my local petshop SWEARS by using acid buffer to bring the pH levels down to a more neutral state.
this only goes to show how little your local petshop knows, and how little you should rely on them for information.
pH and buffering capacity are interrelated; buffering capacity refers to water's ability to maintain a stable pH as acids or bases are added indirectly. bicarbonate (HCO3-), carbonate (CO3-), and in rare instances, hydroxide (OH-) ions are called buffers. If the water has sufficient buffering capacity, it can absorb and neutralize acid without significantly changing the pH. Buffering has both positive and negative consequences. on the plus side, the nitrogen cycle produces nitric acid (nitrate). without buffering, your tank's pH would drop over time (not a good thing). with sufficient buffering, the pH stays stable (a good thing). adding pH reducing chemicals will lower your buffer capacity and result in unstable chemistry.
think of a buffer as a large sponge. as more acid is added, the "sponge" absorbs the acid without changing the pH much. the "sponge's" capacity is limited however and once the buffering capacity is used up, the pH changes more rapidly as acids are added. when you add acid buffer to your water, you'll will deplete the 'sponge' and all of a sudden, your pH will plummet resulting in severe stress to your fish.
morevoer, next water change, you'll be adding alkalinity back to your water and this can result in a yoyo effect, again stressing your fish.
bottom line, leave your pH just the way it comes out of the tap. your fish will be fine.
