Ok. So 25lbs of Re-Fresh shock (calcium hypochlorite granules, 65% available chlorine) in your pool of 12,000 gallons would raise the free chlorine (FC) level to 161ppm and add to the calcium hardness (CH) of your pool water by increasing the CH by 114ppm. It will also raise your pH due to the fact that cal-hypo often has a significant amount of calcium carbonate and calcium hydroxide in it from the manufacturing process. However, it is not so easy to determine the pH rise. That said, your pH is also probably going to be very high as well.
Is this a vinyl pool?
What that pool store told you to do was both dangerous and ill-advised. Water with that much FC in it (and likely very high pH) is extremely irritating to eyes, skin, etc and can bleach clothes and hair. Swimming in water like that (not that you would) can easily make you very sick from the formation of combined chloramines and chloroform when high FC reacts with organics chemical compounds in your skin. It can also be corrosive metal pool equipment. FC that high can easily fade vinyl liners. The good news is, with algae in the water and sunlight, the FC probably did not last very long because it likely got burned off by the sun fairly quickly. Unfortunately, they also raised your CH by quite a lot which could easily cause cloudiness in your pool water form calcium scaling.
SO now you know WHY we distrust pool stores so much on this site - they are often very, very wrong! In this case, dangerously wrong.
How about the DE filter? Did you read my post about adding too much DE? I think you need to take apart your filter and clean it all out again.
Good luck,
Matt
PS - If you do get that pool store manager on the phone, feel free to chew him out for his ignorant employee turning your pool (temporarily) into a toxic chemical spill!! That much calcium hypochlorite is NEVER the right answer under any circumstance unless you're bleaching your whites in the washing machine....