Re: How important is CYA when shocking, other questions, res
When adding calcium chloride to increase the calcium hardness, you usually want to wait 24 hours before retesting the calcium level. Allow the pump to run for at least 8 hours after adding the calcium chloride. Do not add anything else within 8 hours of adding the calcium chloride, especially pH up (sodium carbonate).
I prefer to mix the calcium chloride in a bucket of water first, as this gives a much better result. However, the calcium gets hot as it dissolves and can be dangerous if you mix up too much at one time. As long as you limit the amount of calcium chloride to 1.5 pounds per 4 gallons of water, you won't experience overheating. The mix should turn completely clear and you can pour the mix in front of a return on in the deep end.
Your FC loss over a 24 hour period can be below the testing precision of the test and would therefore register as no loss. If you have FAS-DPD, you can use a larger sample size (25 ml) to get a higher precision of 0.2 ppm or even 0.1 ppm if you use a 50 ml sample size.
During colder weather and/or if the pool is covered, the loss can be fairly low.
20 pounds of calcium chloride dihydrate will raise your calcium hardness by 75 ppm. So, from 225 ppm to 300 ppm. What is your water temperature? What CSI are you going for? You don't want to add too much. You can always add more, but getting it out isn't so easy. I wouldn't go any higher than 300 ppm.