I've never heard of that brand of pH down solution, but I use vinegar in order to lower the pH. As for raising the pH, I use a professional pH up solution of potassium hydroxide.
I just add a capful of vinegar to my water jugs, let them sit for a day, then just water out of the jugs. Capful is just about 6.5 every time I have tested, so I don't have to bother testing each time now. That's close enough for me.
I have used that stuff before. Aquariums are my other hobby and I had some of it laying around and hydro store is an hour away. I used the entire bottle before making the trek and saw no ill affects of it. It is more dilluted than the proffesional ph down so it is not cost effective in my opinion. I got a big *** bottle of ph down for 12 bucks and it will last me years probably. Good luck.