Check out PoolCalculator.com You can use that to Calc how much chems to add for certain situations. We can help you calc it too - but give it a try first.
If you are looking for a good test kit - tftestkits.net is where a lot of us get our gear. Their TF-100 is good value, will last you many years and has the FAS-DPD chlorine test that most kits do not.
I get your pool Gallons somewhere around 11,000 to 13,500 gallons. Depends on how much is shallow end, etc.
1) PH - hard to say how much borax becuase we dont know how far below 6.5 you are. Just target raising 6.3 to 7.5 on the pool calculator and start there. I get 380oz of Borax
2) What is the powdered shock you are using? What Chemical - it'll say Calcium Hypo or Dichlor most likely. Either way - stop adding stabilizer. You dont want too much CYA in the water as it will make your chlorine less effective.
3) Chlorine is something that is continuously used up by the pool (by killing bacteria and algae, or sunlight). So if you are adding chlorine but then can't test for it - it is going somewhere. The short answer is you need to add more chlorine until you've killed off all of the contaminants in the water. There are articles in Pool School on properly shocking the pool.
As to your SWG - it's possible that it is working fine, but cannot keep up with the chlorine needs of the pool because there are things growing in the pool. After completing the shock process you'll be able to better tell if the SWG is producing sufficient chlorine for the pool.