I did use a test strip yesterday just to see where I was at, going from memory:Use the current water depth and diameter to have PoolMath calculate the current gallons, aim for 3-5ppm for the amount of chlorine to add.
You can grab a cheap liquid 3-way test at (see below), that will let you check if there is chlorine and what the PH is. The TF100 will allow you to test all the parameters, but you want to beat back the green right now.
Home Depot Walmart
PH - 6.8-7.0
FC - 0
TA - 80
Stabilizer - 20
I looked at the pool calculator, and based on 6" short of usual water level - it looks like I will need 60oz of 12.5% liquid chlorine to get FC up to 5ppm. Looking at the CYA chart, I would need to double that to get to shock level (10ppm at 20CYA)