Hi CDkoster,
the liquid shock is nothing more than 10 or 12% sodium hypchlorite. Its bleach and nothing more.
the best way to know its a good deal is to use the chlorine calculator that someone linked up for you earlier.
Recommend to call the Pool Store on the phone and ask if they have any before going. If you DO go, do NOT buy anything other than the high % liquid sodium hypochlorite! No more of that powder stuff for you!
Nice job on bringing that CYA down!
With CYA of 40, your FC shock level is 16ppm
http://www.troublefreepool.com/content/128-chlorine-cya-chart-slam-shock
You can calculate how much liquid sodium hypochlorite to add using pool math.
The SLAM is not a one time treatment. You need to get your FC to shock level and keep it there until you pass the 3 slam criteria
1. Overnight Chlorine Loss Test (OCLT)
2. Your CC is < .05
3. You water is clear and you can see the bottom.
It may take several days to completely clear your pool of algae. So, get lots of bleach or liquid shock.
The first day is the most critical. Your FC will not last long at all. Not. at. all. So test every hour or so and bring FC back to slam.
I am concerend also that your Taylor test kit may not have enough FAS-DPD chlorine test regents to complete the slam. Its gonna take a lot of it to measure the FC as often as you will have to. You can get refills at
www.tftestkits.net. Doubtful a pool store will have it, but I suppose you can call and ask.
One last note. Once the FC is above 10, the PH test will be invalid. High FC screws the Ph test up, so disregard it.
Good luck, you are well on your way to getting troublefree.