I just bought a new tub and am having problems keeping my PH below 7.8. It keeps rising to around 8.2 to 8.3. I have been using Leisure Time liquid spa down. My question is can I use Muratic Acid to lower the ph. Are there any other chemicals that can be used to supplement the expensive spa chemicals? Can Baking Soda be used to raise PH?

You got it! You can use muratic acid and baking soda.

In fact, this is what I use and recommend for all the people that come to me with spa chemical questions regarding PH.

You can even use the "ultra" bleach for the chlorine, but it does have a few impurities that sanitizing chlorine doesn't. It's good if you are in a pinch while waiting for that bargain that you won on Ebay to show up.