If you put two gallons of bleach in the pool, how long is it before it drops below 12ppm? At that point is when you need to add more bleach. I suspect that your either never hitting 12ppm or if you are, it's only lasting 15 to 30 mins... If your able to keep it at shock level more often, it's going to take way less time to clear. If that means adding 2 gallons every hour then so be it

You should get some Borax in the pool ASAP, your reading of 6.8 is probably not accurate as that's probably just the lowest the test will measure and it could be much lower... Get it up to about 7.2 if you can as soon as possible, it can damage your pump and other equipment.

PS, you can go to http://www.poolcalculator.com to plug your numbers in and see how much borax to add.