What's your KH? This is a measure of the amount of buffer in the water--basically, an indicator of how stable the pH will be. It sounds like yours is fairly high. This means the chemical additives like pH Down won't work--they might drop the pH a bit, but it will likely bounce back up, especially following a water change. You want to find a way to lower pH so that's it's stable--won't happen with these products.
First though--why do you want to lower it? New tank? Different fish? The existing fish are acclimated to the high pH, and don't need it lower to be fine.
I noticed in your other post that you mentioned you are having a cloudy water issue as well. It might be beneficial to discontinue using pH down, as these type of products typically contain some form of phosphoruos, which is a favorite food of the algae and bacteria that cause cloudy water.
(total side note, but related).
Also, I agree with Orion girl's questions, why are you interested in lowering your pH?
Most fish can live just fine at a less than ideal PH. No fish can live in a tank with wild PH swings. Those addatives are crap, discontinue using them.
Another idea is to keep fish that like high ph. Just a thought...
A high KH can be a good thing. It means that you should have rock solid pH and no worries about swings or crashes. You can inject CO2 with impugnity. Sure, you won't be breeding tetras (or other blackwater fish) and discus probably isn't on your list of fish, but aside from that you're looking pretty good.
Ask your lfs for their tank water params. If they're on the same tap as you then the fish are acclimated to that hardness and pH, I can guarantee you that they're not using any of their own pH down products.
Edit: Punctuation and capitals could make deciphering your question(s) a lot easier. I.e. you'll get the answers you're looking for a lot quicker.