If you are following the directions according to the label on the Ph down and its not doing anything all I can think is that the product might be expired its hard to say. I use sulphuric acid and it works like a charm. 1 to 2 drops per 10 gal of water will lower my Ph a point or 2. There are many products out there that can affect the Ph up or down. Like Baking Soda will cause it to rise for example. I think people that purchase specific products like ph up or ph down are throwing money out the window. I bought some sulphuric acid to lower my ph when needed and I will never have to buy ph down ever and baking soda is so cheap and it raises ph just as well as products advertised for ph up. Just think outside the box theres more than one way to skin a cat. Google ph up and ph down or alternative ways to raise or lower ph. You will be surprised what you find and will save money along the way.

Peace