I'm not Janet, but maybe I'll do! (She is working this evening and it may be tomorrow til she is able to answer, so thought I'd take a crack at it for you.)

If your CYA is at 40 but you still have undissolved stabilizer in the pool, that means that your CYA level is going to go up higher than 40. Therefore, you don't want to use any forms of stabilized chlorine which means no pucks. They are stabilized and will cause your CYA to continue to rise. You also don't want that CYA laying on your liner. Vacuum it up into the filter. Since your CYA is at 40 which is a good level, I'd go ahead and backwash it out.

Since your calcium hardness level is ok you can use cal-hypo for awhile if you want but if it were me, I'd just use bleach. Bleach will never contribute to cloudy water problems.

Did you order a test kit? If not, I'd recommend that you do so. While your water is cloudy, I'd suggest raising your cl up to shock level which would be about 15ppm. In a 20K pool, each gallon (4 quarts) of 6% bleach will add 3ppm of chlorine. Every time you test which should be at least morning and evening for now, add enough bleach to get the cl back up to 15. You need to keep it at shock level until you can go from sundown one evening to sunup the next morning without losing more than 1ppm of chlorine, and you have no more than 0.5ppm of CC (combined chlorine.) Do you have a CC reading by the way? If so, post it. We really need to see it.

Since your pressure gauge hasn't come in yet, you'll have to just judge when to backwash by the pressure of the water coming out of the return. When you feel a substantial decrease in pressure, backwash. Run the pump 24/7 while you are trying to clear the pool.

Not necessary to change out the sand.

Keep working on the pH. You don't have to wait too long between additions of Borax. After adding some, wait a couple of hours, retest and redose. You need to get it above 7.0 ASAP.

Your alk is also low. Add some baking soda to the skimmer to raise it. I'd start with about 3 lbs. at a time. As with the Borax, retest after a few hours and redose until you get somewhere between 80-120. By the way, it is ok to add baking soda, borax and bleach one right after the other.

Hope this helps. Keep us posted how things are going.