Swim University has a video and the guy says to add 3 pounds of shock for a 10,000 gal pool. That's 3x shock level which is also how he describes the strategy. My pool is 10,000 gal marcite with a 8412 cartridge filter. I use DPD chlorine test method. The guys at pinch a penny said it was probably black algae since my pool is pretty old and will need re-marcite soon. I only check chlorine and ph at home. I let the folks at pinch a penny check the other values since I am in there every week. I added 4 lbs of stabilizer a week ago and now it's reading 60. I only use pench a penny liquid chlorine, no tablets. I try to keep my fc between 6 and 8. I add acid or baking soda and calcium etc when they tell me to. Pool looks great right now except for the terrible black spots (lots of them). Temp is 71 deg F though. Too cold for me but I love having my morning bfast and coffee by the pool in the morning and just lounging by it whenever I can.) Mahalo!