i've got a suggestion ... leave your pH alone. your fish will acclimate to it and not suffer the yo-yo effects resulting from the use of chemicals such as pH down.
all water supply, whether municipal or well contains some concentration of calcium and magnesium (among other cations) which typically exist as salts of carbonates. hard water has more of these salts than soft water. these carbonates in solution exhibit a phenomona known as "buffering". when an acid is introduced to a water sample containing carbonates, the carbonates react with the acid and neutralize it, releasing carbon dioxide and a small amount of heat. the CO2 is exhausted at the water surface and the net result is no change in your pH. at some point, the carbonate buffer will become exhausted ... at which time, even a small concentration of acid will rapidly drop the pH of your water and may kill your fish. simply put, carbonates stabilize the pH as long as they are present in sufficient amounts.
in the other direction, i.e adjusting your pH upward, most common chemicals used for the purpose are carbonate salts. they have the effect of increasing many parameters besides pH. adding carbonate buffers to your water will elevate the GH and KH hardness in addition to the pH and Total Dissolved Solids (TDS). while your fish may acclimate to the pH changes you've made artificially, they may not at all appreciate the concurrent changes. moreover, every time you do a water change you dilute those carbonate buffers resulting in a drop in your pH and a change in all those other parameters as well.
it's difficult to stabilize your water chemistry artificially unless you know something about buffers, GH, KH, hydrogen ion concentration, pKA, the effect of higher or lower pH on specific chemistry parameters of your water such as calcium solubility and the toxicity of NH3-NH4 in solution. the stability of the water in your tank is CRITICAL to the health of your fish.
finally ... most of the common fish in the hobby today are tank raised on farms in florida. others may come from private breeders or are imported. in other words, few fish today are wild caught which means that they have become adapted to water chemistry which is outside what might be otherwise considered "normal" for a given species. thus they can be acclimated to a wide range of water chemistry ... and that includes that which comes right out of your tap. there are certain species which will not do well in chemistry outside of their native habitat and if you're going to keep these, you do need to play chemist. Apistogramma are an example. in such cases, RO (Reverse Osmosis) may be an answer, but know what you're getting into.